Variable-focus virtual image devices based on polarization conversion

ABSTRACT

Example display devices include a waveguide configured to propagate visible light under total internal reflection in a direction parallel to a major surface of the waveguide. The waveguide has formed thereon an outcoupling element configured to outcouple a portion of the visible light in a direction normal to the major surface of the waveguide. The example display devices additionally include a polarization-selective notch reflector disposed on a first side of the waveguide and configured to reflect visible light having a first polarization while transmitting the portion of the visible light having a second polarization. The example display devices further include a polarization-independent notch reflector disposed on a second side of the waveguide and configured to reflect visible light having the first polarization and the second polarization, where the polarization-independent notch reflector is configured to convert a polarization of visible light reflecting therefrom.

INCORPORATION BY REFERENCE

This application is a divisional application of U.S. patent applicationSer. No. 15/902,927 filed on Feb. 22, 2018 entitled “VARIABLE-FOCUSVIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION,” which claimsthe priority benefit of U.S. Provisional Patent Application No.62/462,850 filed on Feb. 23, 2017 entitled “VARIABLE-FOCUS VIRTUAL IMAGEDEVICES.” The content of each of these applications is incorporated byreference herein in its entirety. The U.S. Provisional PatentApplication No. 62/462,850 includes the following sections both of whichare incorporated by reference and form a part of this patentapplication:

1. SECTION I: Specification and Drawings for the portion of theapplication entitled “DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR.”

2. SECTION II: Specification and Drawings for the portion of theapplication entitled “VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ONPOLARIZATION CONVERSION.”

Sections I and II of the U.S. Provisional Patent Application No.62/462,850 both discuss variable focus or variable power devices andfeatures associated with the components of these devices and bothSections equally form part of the disclosure of this application.Accordingly, various features, elements, structures, methods, etc.described in Section I can be used with, combined with, incorporatedinto, or are otherwise compatible with features, elements, structures,methods, etc. described in Section II in any combination. Likewise,various features, elements, structures, methods, etc. described inSection II can be used with, combined with, incorporated into, or areotherwise compatible with features, elements, structures, methods, etc.described in Section I in any combination.

This application also incorporates by reference the entirety of each ofthe following patent applications: U.S. application Ser. No. 14/555,585filed on Nov. 27, 2014, now U.S. Pat. No. 9,791,700 B2; U.S. applicationSer. No. 14/690,401 filed on Apr. 18, 2015, now U.S. Pat. No. 10,262,462B2; U.S. application Ser. No. 14/212,961 filed on Mar. 14, 2014, nowU.S. Pat. No. 9,417,452 B2; and U.S. application Ser. No. 14/331,218filed on Jul. 14, 2014, now U.S. Pat. No. 9,671,566 B2.

BACKGROUND Field

The present disclosure relates to display systems and, moreparticularly, to augmented reality display systems comprisingdiffractive devices based at least partly on polarization conversion.

Description of the Related Art

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality” or “augmentedreality” experiences, wherein digitally reproduced images or portionsthereof are presented to a user in a manner wherein they seem to be, ormay be perceived as, real. A virtual reality, or “VR”, scenariotypically involves presentation of digital or virtual image informationwithout transparency to other actual real-world visual input; anaugmented reality, or “AR”, scenario typically involves presentation ofdigital or virtual image information as an augmentation to visualizationof the actual world around the user. A mixed reality, or “MR”, scenariois a type of AR scenario and typically involves virtual objects that areintegrated into, and responsive to, the natural world. For example, inan MR scenario, AR image content may be blocked by or otherwise beperceived as interacting with objects in the real world.

Referring to FIG. 1, an augmented reality scene 1 is depicted wherein auser of an AR technology sees a real-world park-like setting 1100featuring people, trees, buildings in the background, and a concreteplatform 1120. In addition to these items, the user of the AR technologyalso perceives that he “sees” “virtual content” such as a robot statue1110 standing upon the real-world platform 1120, and a cartoon-likeavatar character 1130 flying by which seems to be a personification of abumble bee, even though these elements 1130, 1110 do not exist in thereal world. Because the human visual perception system is complex, it ischallenging to produce an AR technology that facilitates a comfortable,natural-feeling, rich presentation of virtual image elements amongstother virtual or real-world imagery elements.

Systems and methods disclosed herein address various challenges relatedto AR and VR technology.

SUMMARY

This application includes discussions of systems and methods that can beemployed to provide variable optical power. Variable focus or variablepower devices may find application in certain head mounted displaydevices that project images as if the images originated from differentdepths. By changing the optical power of an optical element in the headmounted display device, images presented to the wearer of the headmounted display device appear as if located at different distances fromthe wearer. The variable focus or variable power optical device can thusbe modulated to cause different image content to be displayed as if theimage content is situated at different locations with respect to theuser. Some variable power elements comprise reflectors comprisingmovable membranes. Other variable power elements comprise liquid crystalswitchable devices that can switch between optical power levels usingswitchable liquid crystal elements. Some variable focus devicesdescribed herein utilize the polarization properties of light tofacilitate switching from one focus to another.

In an aspect, a display device comprises a waveguide configured topropagate visible light under total internal reflection in a directionparallel to a major surface of the waveguide; an outcoupling elementformed on the waveguide and configured to outcouple a portion of thevisible light in a direction normal to the major surface of thewaveguide. The display device additionally comprises apolarization-selective notch reflector disposed on a first side of thewaveguide and configured to reflect visible light having a firstpolarization while transmitting the portion of the visible light havinga second polarization. The display device further comprises apolarization-independent notch reflector disposed on a second side ofthe waveguide and configured to reflect visible light having the firstpolarization and the second polarization, wherein thepolarization-independent notch reflector is configured to convert apolarization of visible light reflecting therefrom.

In another aspect, a display device comprises a wave-guiding deviceinterposed between a first switchable lens and a second switchable lens,wherein the wave-guiding device comprises one or more cholesteric liquidcrystal (CLC) layers each comprising a plurality of chiral structures,wherein each chiral structure comprises a plurality of liquid crystalmolecules that extend in a layer depth direction and are successivelyrotated in a first rotation direction, wherein arrangements of theliquid crystal molecules of the chiral structures vary periodically in alateral direction perpendicular to the layer depth direction such thatthe one or more CLC layers are configured to Bragg-reflect incidentlight. The wave-guiding device additionally includes one or morewaveguides formed over the one or more CLC layers and configured topropagate visible light under total internal reflection (TIR) in adirection parallel to a major surface of the waveguide and to opticallycouple visible light to or from the one or more CLC layers.

In another aspect, a display device configured to display an image to aneye of a user comprises an optical display. The optical display has aforward side and a rearward side, where the rearward side is closer tothe eye of the user than the forward side. The optical display isconfigured to output light having a wavelength range toward the rearwardside. A first notch reflector is disposed rearward of the opticaldisplay, the first notch reflector configured to reflect light havingthe wavelength range output from the optical display. A second notchreflector is disposed forward of the optical display, the second notchreflector configured to reflect light having the wavelength range. Thefirst notch reflector is configured to substantially transmit lighthaving a first polarization and substantially reflect light having asecond polarization that is different from the first polarization. Thesecond notch reflector is configured to convert light incident on arearward face having the second polarization to the first polarizationand to redirect the light rearward.

In another aspect, a dynamically focused display system comprises adisplay configured to output circularly polarized light in a firstcircular polarization state. The display is disposed along an opticalaxis and has a forward side and a rearward side, the rearward sidecloser to the eye of the user than the forward side, the optical displayconfigured to output light having a wavelength range toward the rearwardside. A first switchable optical element is disposed along the opticalaxis, the first switchable optical element configured to change thecircular polarization state of light transmitted through the firstswitchable optical element from the first circular polarization state toa second, different, circular polarization state. A first cholestericliquid crystal (CLC) lens is disposed forward of the first switchableoptical element along the optical axis. A second switchable opticalelement is disposed forward of the first CLC lens along the opticalaxis, the second switchable optical element configured to change thecircular polarization state of light transmitted through the secondswitchable optical element from the first circular polarization state toa second, different, circular polarization state. A second CLC lensdisposed forward of the second switchable optical element along theoptical axis. A controller is configured to electronically switch thestates of the first and the second switchable optical elements todynamically select either the first CLC lens or the second CLC lens.

In another aspect, aspect, a wearable augmented reality head-mounteddisplay system is configured to pass light from the world forward awearer wearing the head-mounted system into an eye of the wearer. Thewearable augmented reality head mounted display system comprises anoptical display configured to output light to form an image; one or morewaveguides disposed to receiving said light from said display; a frameconfigured to dispose the waveguides forward of said eye such that saidone or more waveguides have a forward side and a rearward side, saidrearward said closer to said eye than said forward side; a cholestericliquid crystal (CLC) reflector disposed on said forward side of said oneor more waveguides, said CLC reflector configured to have an opticalpower or a depth of focus that is adjustable upon application of anelectrical signal; and one or more out-coupling elements disposed withrespect to said one or more waveguides to extract light from the one ormore waveguides and direct at least a portion of said light propagatingwithin said waveguide to the CLC reflector, said light being directedfrom said CLC reflector back through said waveguide and into said eye topresent an image from the display into the eye of the wearer.

In another aspect, a display device comprises a waveguide configured topropagate visible light under total internal reflection in a directionparallel to a major surface of the waveguide and to outcouple thevisible light in a direction normal to the major surface. A notchreflector is configured to reflect visible light having a firstpolarization, wherein the notch reflector comprises one or morecholesteric liquid crystal (CLC) layers, wherein each of the CLC layerscomprises a plurality of chiral structures, wherein each of the chiralstructures comprises a plurality of liquid crystal molecules that extendin a layer depth direction and are successively rotated in a firstrotation direction, wherein arrangements of the liquid crystal moleculesof the chiral structures vary periodically in a lateral directionperpendicular to the layer depth direction such that the one or more CLClayers are configured to Bragg-reflect incident light.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Neitherthis summary nor the following detailed description purports to defineor limit the scope of the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a user's view of augmented reality (AR) through an ARdevice.

FIG. 2 illustrates an example of wearable display system.

FIG. 3 illustrates a conventional display system for simulatingthree-dimensional imagery for a user.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes.

FIGS. 5A-5C illustrate relationships between radius of curvature andfocal radius.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user.

FIG. 7 illustrates an example of exit beams outputted by a waveguide.

FIG. 8 illustrates an example of a stacked waveguide assembly in whicheach depth plane includes images formed using multiple differentcomponent colors.

FIG. 9A illustrates a cross-sectional side view of an example of a setof stacked waveguides that each includes an incoupling optical element.

FIG. 9B illustrates a perspective view of an example of the plurality ofstacked waveguides of FIG. 9A.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B.

FIG. 10 illustrates a cross-sectional side view of an example of acholesteric liquid crystal diffraction grating (CLCG) having a pluralityof uniform chiral structures.

FIG. 11 illustrates a cross-sectional side view of an example of a CLCGhaving differently arranged chiral structures in a lateral direction.

FIG. 12 illustrates a cross-sectional side view of an example of a CLClayer configured for Bragg reflection at an off-axis incident angle.

FIG. 13A illustrates a cross-sectional side view of an example of a CLClayer having a first helical pitch and configured for Bragg-reflectionat a first off-axis incident angle.

FIG. 13B illustrates a cross-sectional side view of an example of a CLClayer having a second helical pitch and configured for Bragg-reflectionat a second off-axis incident angle.

FIG. 13C illustrates a cross-sectional side view of an example of a CLCGincluding CLC layers of FIGS. 13A and 13B having different helicalpitches in a stacked configuration for Bragg-reflection at a pluralityof off-axis incident angles and high diffraction bandwidth.

FIG. 14 illustrates a cross-sectional side view of an example of a CLCGincluding a CLC layer having vertical regions with different helicalpitches along a depth direction for Bragg-reflection at a plurality ofoff-axis incident angles and high diffraction bandwidth.

FIG. 15 illustrates a cross-sectional side view of an example of a CLCGincluding a CLC layer having lateral regions with different helicalpitches along a lateral direction for spatially varyingBragg-reflection.

FIG. 16 illustrates an example of an optical wave-guiding devicecomprising a waveguide coupled to a CLCG and configured to propagatelight by total internal reflection (TIR).

FIG. 17A illustrates an example of an optical wave-guiding devicecomprising a waveguide coupled to a CLCG and configured to selectivelypropagate light having a wavelength by total internal reflection (TIR).

FIG. 17B illustrates an example of a plurality of optical wave-guidingdevices in the same optical path, each comprising a waveguide coupled toa CLCG and configured to selectively propagate light having a wavelengthby total internal reflection (TIR).

FIG. 17C illustrates an example of a plurality of optical wave-guidingdevices in the same optical path, each comprising a waveguide coupled toa CLCG and configured to selectively propagate light having a wavelengthby total internal reflection (TIR).

FIG. 18 illustrates an example of an optical wave-guiding devicecomprising a common waveguide coupled to a plurality of CLCGs andconfigured to selectively propagate light having a plurality ofwavelengths by total internal reflection (TIR).

FIG. 19 illustrates an example of an optical wave-guiding devicecomprising a waveguide coupled to a CLCG and configured to propagatelight by total internal reflection (TIR).

FIG. 20 illustrates an example of an optical wave-guiding devicecomprising a waveguide coupled to a CLCG and a polarization convertingreflector, where the CLCG is configured to receive incident light andthe waveguide is configured to propagate light Bragg-reflected from theCLCG by total internal reflection (TIR).

FIG. 21A illustrates the optical wave-guiding device of FIG. 20, wherethe CLCG is configured to receive incident light that is linearlypolarized or unpolarized, and where the waveguide is configured topropagate light Bragg-reflected from the CLCG and light reflected by thereflector by total internal reflection (TIR).

FIG. 21B illustrates the optical wave-guiding device of FIG. 20, wherethe CLCG configured to receive incident light that is polarized intoorthogonal elliptical or circular polarized light beams, and where thewaveguide is configured to propagate light Bragg-reflected from the CLCGand light reflected by the reflector by total internal reflection (TIR).

FIG. 22A illustrates an example of an optical wave-guiding devicecomprising a plurality of CLC layers coupled to a common waveguide,including a first CLC layer having chiral structures having a firstrotation direction and a second CLC layer having chiral structureshaving a second rotation direction opposite to the first rotationdirection, under a condition in which the incident light beam islinearly polarized or unpolarized.

FIG. 22B illustrates the optical wave-guiding device of FIG. 22A, undera condition in which the incident light is polarized into orthogonalelliptical or circular polarized light beams.

FIG. 22C illustrates an example of an optical wave-guiding devicecomprising a plurality of CLC layers coupled to a common waveguideinterposed between two CLC layers, including a first CLC layer havingchiral structures having a first rotation direction and a second CLClayer having chiral structures having a second rotation directionopposite to the first rotation direction, under a condition in which theincident light beam is linearly polarized or unpolarized.

FIG. 23 illustrates an example of an imaging system comprising aforward-facing camera configured to images a wearer's eye using acholesteric liquid crystal (CLC) off-axis mirror.

FIGS. 24A-24F illustrate examples of imaging systems comprising aforward-facing camera configured to images a wearer's eye using a CLCoff-axis mirror.

FIGS. 24G and 24H illustrate examples of imaging systems comprising aforward-facing camera configured to images a wearer's eye using adiffractive optical element comprising a plurality of segments includingone more CLC off-axis mirrors, where each of the segments can havedifferent optical properties.

FIG. 25A illustrates an example display device comprising a polarizationconverter and configured to output an image to a user.

FIG. 25B illustrates an example display device comprising a polarizationconverter and configured to output image to a user.

FIG. 26A illustrates an example display device comprising a polarizationconverter and a switchable lens, and configured to output virtual imageto a user.

FIG. 26B illustrates an example display device comprising a polarizationconverter and a switchable lens, and configured to output a real imageto a user.

FIG. 26C illustrates an example display device comprising a polarizationconverter and a switchable lens, and configured to output virtual imageto a user.

FIG. 26D illustrates an example display device comprising a polarizationconverter and a switchable lens, and configured to output a real imageto a user.

FIG. 27A illustrates an example display device comprising a polarizationconverter and a Pancharatnam-Barry (PB) lens, and configured to outputvirtual image to a user.

FIG. 27B illustrates an example display device comprising a polarizationconverter and a PB lens, and configured to output a real image to auser.

FIG. 27C illustrates an example display device comprising a polarizationconverter and a PB lens, and configured to output virtual image to auser.

FIG. 27D illustrates an example display device comprising a polarizationconverter and a PB lens, and configured to output a real image to auser.

FIG. 28A illustrates a spatial off-set created by two orthogonalpolarization images formed by an example display device comprising apolarization converter and a PB lens.

FIG. 28B illustrates an example offset compensator comprising a pair oflenses for compensating the spatial off-set illustrated in FIG. 28A.

FIG. 28C illustrates a negation effect of the spatial off-setillustrated in FIG. 28A using an embodiment of the offset compensatorillustrated in FIG. 28B.

FIG. 29 illustrates an example display device comprising a waveguideassembly configured to asymmetrically project light and PB lenses, andconfigured to output image to a user.

FIG. 30 illustrates an example display device comprising a waveguideassembly having a CLCG and a deformable mirror, and configured to outputimage to a user.

FIGS. 31A-31C illustrate example reflective diffraction lenses that canbe implemented as part of a display device, where the reflectivediffraction lenses are formed of patterned CLC materials serving as areflective polarizing mirror.

FIG. 32A illustrates an example of chromatic aberration observed indiffractive lenses.

FIG. 32B illustrates an example reflective diffraction lens comprising aplurality of reflective diffraction lenses in a stacked configuration.

FIGS. 33A-33D illustrates example reflective diffraction lens assembliesand their operation for dynamic switching between different focaldistances.

FIG. 34 illustrates an example combination of waveguide assemblycomprising an eyepiece configured to direct light world-ward and a CLClens configured to re-direct the light eye-ward.

Throughout the drawings, reference numbers may be re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate example embodiments described herein and are not intended tolimit the scope of the disclosure.

DETAILED DESCRIPTION

AR systems may display virtual content to a user, or viewer, while stillallowing the user to see the world around them. Preferably, this contentis displayed on a head-mounted display, e.g., as part of eyewear, thatprojects image information to the user's eyes. In addition, the displaymay also transmit light from the surrounding environment to the user'seyes, to allow a view of that surrounding environment. As used herein,it will be appreciated that a “head-mounted” display is a display thatmay be mounted on the head of a viewer.

FIG. 2 illustrates an example of wearable display system 80. The displaysystem 80 includes a display 62, and various mechanical and electronicmodules and systems to support the functioning of that display 62. Thedisplay 62 may be coupled to a frame 64, which is wearable by a displaysystem user or viewer 60 and which is configured to position the display62 in front of the eyes of the user 60. The display 62 may be consideredeyewear in some embodiments. In some embodiments, a speaker 66 iscoupled to the frame 64 and positioned adjacent the ear canal of theuser 60 (in some embodiments, another speaker, not shown, is positionedadjacent the other ear canal of the user to provide for stereo/shapeablesound control). In some embodiments, the display system may also includeone or more microphones 67 or other devices to detect sound. In someembodiments, the microphone is configured to allow the user to provideinputs or commands to the system 80 (e.g., the selection of voice menucommands, natural language questions, etc.), and/or may allow audiocommunication with other persons (e.g., with other users of similardisplay systems. The microphone may further be configured as aperipheral sensor to continuously collect audio data (e.g., to passivelycollect from the user and/or environment). Such audio data may includeuser sounds such as heavy breathing, or environmental sounds, such as aloud bang indicative of a nearby event. The display system may alsoinclude a peripheral sensor 30 a, which may be separate from the frame64 and attached to the body of the user 60 (e.g., on the head, torso, anextremity, etc. of the user 60). The peripheral sensor 30 a may beconfigured to acquire data characterizing the physiological state of theuser 60 in some embodiments, as described further herein. For example,the sensor 30 a may be an electrode.

With continued reference to FIG. 2, the display 62 is operativelycoupled by communications link 68, such as by a wired lead or wirelessconnectivity, to a local data processing module 70 which may be mountedin a variety of configurations, such as fixedly attached to the frame64, fixedly attached to a helmet or hat worn by the user, embedded inheadphones, or otherwise removably attached to the user 60 (e.g., in abackpack-style configuration, in a belt-coupling style configuration).Similarly, the sensor 30 a may be operatively coupled by communicationslink 30 b, e.g., a wired lead or wireless connectivity, to the localprocessor and data module 70. The local processing and data module 70may comprise a hardware processor, as well as digital memory, such asnon-volatile memory (e.g., flash memory or hard disk drives), both ofwhich may be utilized to assist in the processing, caching, and storageof data. The data include data a) captured from sensors (which may be,e.g., operatively coupled to the frame 64 or otherwise attached to theuser 60), such as image capture devices (such as cameras), microphones,inertial measurement units, accelerometers, compasses, GPS units, radiodevices, gyros, and/or other sensors disclosed herein; and/or b)acquired and/or processed using remote processing module 72 and/orremote data repository 74 (including data relating to virtual content),possibly for passage to the display 62 after such processing orretrieval. The local processing and data module 70 may be operativelycoupled by communication links 76, 78, such as via a wired or wirelesscommunication links, to the remote processing module 72 and remote datarepository 74 such that these remote modules 72, 74 are operativelycoupled to each other and available as resources to the local processingand data module 70. In some embodiments, the local processing and datamodule 70 may include one or more of the image capture devices,microphones, inertial measurement units, accelerometers, compasses, GPSunits, radio devices, and/or gyros. In some other embodiments, one ormore of these sensors may be attached to the frame 64, or may bestandalone structures that communicate with the local processing anddata module 70 by wired or wireless communication pathways.

With continued reference to FIG. 2, in some embodiments, the remoteprocessing module 72 may comprise one or more processors configured toanalyze and process data and/or image information. In some embodiments,the remote data repository 74 may comprise a digital data storagefacility, which may be available through the internet or othernetworking configuration in a “cloud” resource configuration. In someembodiments, the remote data repository 74 may include one or moreremote servers, which provide information, e.g., information forgenerating augmented reality content, to the local processing and datamodule 70 and/or the remote processing module 72. In some embodiments,all data is stored and all computations are performed in the localprocessing and data module, allowing fully autonomous use from a remotemodule.

The perception of an image as being “three-dimensional” or “3-D” may beachieved by providing slightly different presentations of the image toeach eye of the viewer. FIG. 3 illustrates a conventional display systemfor simulating three-dimensional imagery for a user. Two distinct images5, 7—one for each eye 4, 6—are outputted to the user. The images 5, 7are spaced from the eyes 4, 6 by a distance 10 along an optical orz-axis parallel to the line of sight of the viewer. The images 5, 7 areflat and the eyes 4, 6 may focus on the images by assuming a singleaccommodated state. Such systems rely on the human visual system tocombine the images 5, 7 to provide a perception of depth and/or scalefor the combined image.

It will be appreciated, however, that the human visual system is morecomplicated and providing a realistic perception of depth is morechallenging. For example, many viewers of conventional “3-D” displaysystems find such systems to be uncomfortable or may not perceive asense of depth at all. Without being limited by theory, it is believedthat viewers of an object may perceive the object as being“three-dimensional” due to a combination of vergence and accommodation.Vergence movements (i.e., rotation of the eyes so that the pupils movetoward or away from each other to converge the lines of sight of theeyes to fixate upon an object) of the two eyes relative to each otherare closely associated with focusing (or “accommodation”) of the lensesand pupils of the eyes. Under normal conditions, changing the focus ofthe lenses of the eyes, or accommodating the eyes, to change focus fromone object to another object at a different distance will automaticallycause a matching change in vergence to the same distance, under arelationship known as the “accommodation-vergence reflex,” as well aspupil dilation or constriction. Likewise, a change in vergence willtrigger a matching change in accommodation of lens shape and pupil size,under normal conditions. As noted herein, many stereoscopic or “3-D”display systems display a scene using slightly different presentations(and, so, slightly different images) to each eye such that athree-dimensional perspective is perceived by the human visual system.Such systems are uncomfortable for many viewers, however, since they,among other things, simply provide a different presentation of a scene,but with the eyes viewing all the image information at a singleaccommodated state, and work against the “accommodation-vergencereflex.” Display systems that provide a better match betweenaccommodation and vergence may form more realistic and comfortablesimulations of three-dimensional imagery contributing to increasedduration of wear and in turn compliance to diagnostic and therapyprotocols.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes. With reference toFIG. 4, objects at various distances from eyes 4, 6 on the z-axis areaccommodated by the eyes 4, 6 so that those objects are in focus. Theeyes (4 and 6) assume particular accommodated states to bring into focusobjects at different distances along the z-axis. Consequently, aparticular accommodated state may be said to be associated with aparticular one of depth planes 14, with has an associated focaldistance, such that objects or parts of objects in a particular depthplane are in focus when the eye is in the accommodated state for thatdepth plane. In some embodiments, three-dimensional imagery may besimulated by providing different presentations of an image for each ofthe eyes 4, 6, and also by providing different presentations of theimage corresponding to each of the depth planes. While shown as beingseparate for clarity of illustration, it will be appreciated that thefields of view of the eyes 4, 6 may overlap, for example, as distancealong the z-axis increases. In addition, while shown as flat for ease ofillustration, it will be appreciated that the contours of a depth planemay be curved in physical space, such that all features in a depth planeare in focus with the eye in a particular accommodated state.

The distance between an object and the eye 4 or 6 may also change theamount of divergence of light from that object, as viewed by that eye.FIGS. 5A-5C illustrates relationships between distance and thedivergence of light rays. The distance between the object and the eye 4is represented by, in order of decreasing distance, R1, R2, and R3. Asshown in FIGS. 5A-5C, the light rays become more divergent as distanceto the object decreases. As distance increases, the light rays becomemore collimated. Stated another way, it may be said that the light fieldproduced by a point (the object or a part of the object) has a sphericalwavefront curvature, which is a function of how far away the point isfrom the eye of the user. The curvature increases with decreasingdistance between the object and the eye 4. Consequently, at differentdepth planes, the degree of divergence of light rays is also different,with the degree of divergence increasing with decreasing distancebetween depth planes and the viewer's eye 4. While only a single eye 4is illustrated for clarity of illustration in FIGS. 5A-5C and otherfigures herein, it will be appreciated that the discussions regardingeye 4 may be applied to both eyes 4 and 6 of a viewer.

Without being limited by theory, it is believed that the human eyetypically can interpret a finite number of depth planes to provide depthperception. Consequently, a highly believable simulation of perceiveddepth may be achieved by providing, to the eye, different presentationsof an image corresponding to each of these limited number of depthplanes. The different presentations may be separately focused by theviewer's eyes, thereby helping to provide the user with depth cues basedon the accommodation of the eye required to bring into focus differentimage features for the scene located on different depth plane and/orbased on observing different image features on different depth planesbeing out of focus.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user. A display system 1000 includes a stack ofwaveguides, or stacked waveguide assembly, 1178 that may be utilized toprovide three-dimensional perception to the eye/brain using a pluralityof waveguides 1182, 1184, 1186, 1188, 1190. In some embodiments, thedisplay system 1000 is the system 80 of FIG. 2, with FIG. 6schematically showing some parts of that system 80 in greater detail.For example, the waveguide assembly 1178 may be part of the display 62of FIG. 2. It will be appreciated that the display system 1000 may beconsidered a light field display in some embodiments.

With continued reference to FIG. 6, the waveguide assembly 1178 may alsoinclude a plurality of features 1198, 1196, 1194, 1192 between thewaveguides. In some embodiments, the features 1198, 1196, 1194, 1192 maybe one or more lenses. The waveguides 1182, 1184, 1186, 1188, 1190and/or the plurality of lenses 1198, 1196, 1194, 1192 may be configuredto send image information to the eye with various levels of wavefrontcurvature or light ray divergence. Each waveguide level may beassociated with a particular depth plane and may be configured to outputimage information corresponding to that depth plane. Image injectiondevices 1200, 1202, 1204, 1206, 1208 may function as a source of lightfor the waveguides and may be utilized to inject image information intothe waveguides 1182, 1184, 1186, 1188, 1190, each of which may beconfigured, as described herein, to distribute incoming light acrosseach respective waveguide, for output toward the eye 4. Light exits anoutput surface 1300, 1302, 1304, 1306, 1308 of the image injectiondevices 1200, 1202, 1204, 1206, 1208 and is injected into acorresponding input surface 1382, 1384, 1386, 1388, 1390 of thewaveguides 1182, 1184, 1186, 1188, 1190. In some embodiments, the eachof the input surfaces 1382, 1384, 1386, 1388, 1390 may be an edge of acorresponding waveguide, or may be part of a major surface of thecorresponding waveguide (that is, one of the waveguide surfaces directlyfacing the world 1144 or the viewer's eye 4). In some embodiments, asingle beam of light (e.g. a collimated beam) may be injected into eachwaveguide to output an entire field of cloned collimated beams that aredirected toward the eye 4 at particular angles (and amounts ofdivergence) corresponding to the depth plane associated with aparticular waveguide. In some embodiments, a single one of the imageinjection devices 1200, 1202, 1204, 1206, 1208 may be associated withand inject light into a plurality (e.g., three) of the waveguides 1182,1184, 1186, 1188, 1190.

In some embodiments, the image injection devices 1200, 1202, 1204, 1206,1208 are discrete displays that each produce image information forinjection into a corresponding waveguide 1182, 1184, 1186, 1188, 1190,respectively. In some other embodiments, the image injection devices1200, 1202, 1204, 1206, 1208 are the output ends of a single multiplexeddisplay which may, e.g., pipe image information via one or more opticalconduits (such as fiber optic cables) to each of the image injectiondevices 1200, 1202, 1204, 1206, 1208. It will be appreciated that theimage information provided by the image injection devices 1200, 1202,1204, 1206, 1208 may include light of different wavelengths, or colors(e.g., different component colors, as discussed herein).

In some embodiments, the light injected into the waveguides 1182, 1184,1186, 1188, 1190 is provided by a light projector system 2000, whichcomprises a light module 2040, which may include a light emitter, suchas a light emitting diode (LED). The light from the light module 2040may be directed to and modified by a light modulator 2030, e.g., aspatial light modulator, via a beam splitter 2050. The light modulator2030 may be configured to change the perceived intensity of the lightinjected into the waveguides 1182, 1184, 1186, 1188, 1190. Examples ofspatial light modulators include liquid crystal displays (LCD) includinga liquid crystal on silicon (LCOS) displays.

In some embodiments, the display system 1000 may be a scanning fiberdisplay comprising one or more scanning fibers configured to projectlight in various patterns (e.g., raster scan, spiral scan, Lissajouspatterns, etc.) into one or more waveguides 1182, 1184, 1186, 1188, 1190and ultimately to the eye 4 of the viewer. In some embodiments, theillustrated image injection devices 1200, 1202, 1204, 1206, 1208 mayschematically represent a single scanning fiber or a bundles of scanningfibers configured to inject light into one or a plurality of thewaveguides 1182, 1184, 1186, 1188, 1190. In some other embodiments, theillustrated image injection devices 1200, 1202, 1204, 1206, 1208 mayschematically represent a plurality of scanning fibers or a plurality ofbundles of scanning, fibers each of which are configured to inject lightinto an associated one of the waveguides 1182, 1184, 1186, 1188, 1190.It will be appreciated that the one or more optical fibers may beconfigured to transmit light from the light module 2040 to the one ormore waveguides 1182, 1184, 1186, 1188, 1190. It will be appreciatedthat one or more intervening optical structures may be provided betweenthe scanning fiber, or fibers, and the one or more waveguides 1182,1184, 1186, 1188, 1190 to, e.g., redirect light exiting the scanningfiber into the one or more waveguides 1182, 1184, 1186, 1188, 1190.

A controller 1210 controls the operation of one or more of the stackedwaveguide assembly 1178, including operation of the image injectiondevices 1200, 1202, 1204, 1206, 1208, the light source 2040, and thelight modulator 2030. In some embodiments, the controller 1210 is partof the local data processing module 70. The controller 1210 includesprogramming (e.g., instructions in a non-transitory medium) thatregulates the timing and provision of image information to thewaveguides 1182, 1184, 1186, 1188, 1190 according to, e.g., any of thevarious schemes disclosed herein. In some embodiments, the controllermay be a single integral device, or a distributed system connected bywired or wireless communication channels. The controller 1210 may bepart of the processing modules 70 or 72 (FIG. 1) in some embodiments.

With continued reference to FIG. 6, the waveguides 1182, 1184, 1186,1188, 1190 may be configured to propagate light within each respectivewaveguide by total internal reflection (TIR). The waveguides 1182, 1184,1186, 1188, 1190 may each be planar or have another shape (e.g.,curved), with major top and bottom surfaces and edges extending betweenthose major top and bottom surfaces. In the illustrated configuration,the waveguides 1182, 1184, 1186, 1188, 1190 may each include outcouplingoptical elements 1282, 1284, 1286, 1288, 1290 that are configured toextract light out of a waveguide by redirecting the light, propagatingwithin each respective waveguide, out of the waveguide to output imageinformation to the eye 4. Extracted light may also be referred to asoutcoupled light and the outcoupling optical elements light may also bereferred to light extracting optical elements. An extracted beam oflight is outputted by the waveguide at locations at which the lightpropagating in the waveguide strikes a light extracting optical element.The outcoupling optical elements 1282, 1284, 1286, 1288, 1290 may, forexample, be gratings, including diffractive optical features, asdiscussed further herein. While illustrated disposed at the bottom majorsurfaces of the waveguides 1182, 1184, 1186, 1188, 1190 for ease ofdescription and drawing clarity, in some embodiments, the outcouplingoptical elements 1282, 1284, 1286, 1288, 1290 may be disposed at the topand/or bottom major surfaces, and/or may be disposed directly in thevolume of the waveguides 1182, 1184, 1186, 1188, 1190, as discussedfurther herein. In some embodiments, the outcoupling optical elements1282, 1284, 1286, 1288, 1290 may be formed in a layer of material thatis attached to a transparent substrate to form the waveguides 1182,1184, 1186, 1188, 1190. In some other embodiments, the waveguides 1182,1184, 1186, 1188, 1190 may be a monolithic piece of material and theoutcoupling optical elements 1282, 1284, 1286, 1288, 1290 may be formedon a surface and/or in the interior of that piece of material.

With continued reference to FIG. 6, as discussed herein, each waveguide1182, 1184, 1186, 1188, 1190 is configured to output light to form animage corresponding to a particular depth plane. For example, thewaveguide 1182 nearest the eye may be configured to deliver collimatedlight, as injected into such waveguide 1182, to the eye 4. Thecollimated light may be representative of the optical infinity focalplane. The next waveguide up 1184 may be configured to send outcollimated light which passes through the first lens 1192 (e.g., anegative lens) before it can reach the eye 4; such first lens 1192 maybe configured to create a slight convex wavefront curvature so that theeye/brain interprets light coming from that next waveguide up 1184 ascoming from a first focal plane closer inward toward the eye 4 fromoptical infinity. Similarly, the third up waveguide 1186 passes itsoutput light through both the first 1192 and second 1194 lenses beforereaching the eye 4; the combined optical power of the first 1192 andsecond 1194 lenses may be configured to create another incrementalamount of wavefront curvature so that the eye/brain interprets lightcoming from the third waveguide 1186 as coming from a second focal planethat is even closer inward toward the person from optical infinity thanwas light from the next waveguide up 1184.

The other waveguide layers 1188, 1190 and lenses 1196, 1198 aresimilarly configured, with the highest waveguide 1190 in the stacksending its output through all of the lenses between it and the eye foran aggregate focal power representative of the closest focal plane tothe person. To compensate for the stack of lenses 1198, 1196, 1194, 1192when viewing/interpreting light coming from the world 1144 on the otherside of the stacked waveguide assembly 1178, a compensating lens layer1180 may be disposed at the top of the stack to compensate for theaggregate power of the lens stack 1198, 1196, 1194, 1192 below. Such aconfiguration provides as many perceived focal planes as there areavailable waveguide/lens pairings. Both the outcoupling optical elementsof the waveguides and the focusing aspects of the lenses may be static(i.e., not dynamic or electro-active). In some alternative embodiments,either or both may be dynamic using electro-active features.

In some embodiments, two or more of the waveguides 1182, 1184, 1186,1188, 1190 may have the same associated depth plane. For example,multiple waveguides 1182, 1184, 1186, 1188, 1190 may be configured tooutput images set to the same depth plane, or multiple subsets of thewaveguides 1182, 1184, 1186, 1188, 1190 may be configured to outputimages set to the same plurality of depth planes, with one set for eachdepth plane. This can provide advantages for forming a tiled image toprovide an expanded field of view at those depth planes.

With continued reference to FIG. 6, the outcoupling optical elements1282, 1284, 1286, 1288, 1290 may be configured to both redirect lightout of their respective waveguides and to output this light with theappropriate amount of divergence or collimation for a particular depthplane associated with the waveguide. As a result, waveguides havingdifferent associated depth planes may have different configurations ofoutcoupling optical elements 1282, 1284, 1286, 1288, 1290, which outputlight with a different amount of divergence depending on the associateddepth plane. In some embodiments, the light extracting optical elements1282, 1284, 1286, 1288, 1290 may be volumetric or surface features,which may be configured to output light at specific angles. For example,the light extracting optical elements 1282, 1284, 1286, 1288, 1290 maybe volume holograms, surface holograms, and/or diffraction gratings. Insome embodiments, the features 1198, 1196, 1194, 1192 may not be lenses;rather, they may simply be spacers (e.g., cladding layers and/orstructures for forming air gaps).

In some embodiments, the outcoupling optical elements 1282, 1284, 1286,1288, 1290 are diffractive features that form a diffraction pattern, or“diffractive optical element” (also referred to herein as a “DOE”).Preferably, the DOE's have a sufficiently low diffraction efficiency (aratio of diffracted beam intensity to the incident beam intensity) sothat only a portion of the light of the beam is deflected away towardthe eye 4 with each intersection of the DOE, while the rest continues tomove through a waveguide via total internal reflection. The lightcarrying the image information is thus divided into a number of relatedexit beams that exit the waveguide at a multiplicity of locations andthe result is a fairly uniform pattern of exit emission toward the eye 4for this particular collimated beam bouncing around within a waveguide.

In some embodiments, one or more DOEs may be switchable between “on”states in which they actively diffract, and “off” states in which theydo not significantly diffract. For instance, a switchable DOE maycomprise a layer of polymer dispersed liquid crystal, in whichmicrodroplets comprise a diffraction pattern in a host medium, and therefractive index of the microdroplets may be switched to substantiallymatch the refractive index of the host material (in which case thepattern does not appreciably diffract incident light) or themicrodroplet may be switched to an index that does not match that of thehost medium (in which case the pattern actively diffracts incidentlight).

In some embodiments, a camera assembly 500 (e.g., a digital camera,including visible light and infrared light cameras) may be provided tocapture images of the eye 4 and/or tissue around the eye 4 to, e.g.,detect user inputs and/or to monitor the physiological state of theuser. As used herein, a camera may be any image capture device. In someembodiments, the camera assembly 500 may include an image capture deviceand a light source to project light (e.g., infrared light) to the eye,which may then be reflected by the eye and detected by the image capturedevice. In some embodiments, the camera assembly 500 may be attached tothe frame 64 (FIG. 2) and may be in electrical communication with theprocessing modules 70 and/or 72, which may process image informationfrom the camera assembly 500 to make various determinations regarding,e.g., the physiological state of the user, as discussed herein. It willbe appreciated that information regarding the physiological state ofuser may be used to determine the behavioral or emotional state of theuser. Examples of such information include movements of the user and/orfacial expressions of the user. The behavioral or emotional state of theuser may then be triangulated with collected environmental and/orvirtual content data so as to determine relationships between thebehavioral or emotional state, physiological state, and environmental orvirtual content data. In some embodiments, one camera assembly 500 maybe utilized for each eye, to separately monitor each eye.

With reference now to FIG. 7, an example of exit beams outputted by awaveguide is shown. One waveguide is illustrated, but it will beappreciated that other waveguides in the waveguide assembly 1178 (FIG.6) may function similarly, where the waveguide assembly 1178 includesmultiple waveguides. Light 400 is injected into the waveguide 1182 atthe input surface 1382 of the waveguide 1182 and propagates within thewaveguide 1182 by TIR. At points where the light 400 impinges on the DOE1282, a portion of the light exits the waveguide as exit beams 402. Theexit beams 402 are illustrated as substantially parallel but, asdiscussed herein, they may also be redirected to propagate to the eye 4at an angle (e.g., forming divergent exit beams), depending on the depthplane associated with the waveguide 1182. It will be appreciated thatsubstantially parallel exit beams may be indicative of a waveguide withoutcoupling optical elements that outcouple light to form images thatappear to be set on a depth plane at a large distance (e.g., opticalinfinity) from the eye 4. Other waveguides or other sets of outcouplingoptical elements may output an exit beam pattern that is more divergent,which would require the eye 4 to accommodate to a closer distance tobring it into focus on the retina and would be interpreted by the brainas light from a distance closer to the eye 4 than optical infinity.

In some embodiments, a full color image may be formed at each depthplane by overlaying images in each of the component colors, e.g., threeor more component colors. FIG. 8 illustrates an example of a stackedwaveguide assembly in which each depth plane includes images formedusing multiple different component colors. The illustrated embodimentshows depth planes 14 a-14 f, although more or fewer depths are alsocontemplated. Each depth plane may have three component color imagesassociated with it: a first image of a first color, G; a second image ofa second color, R; and a third image of a third color, B. Differentdepth planes are indicated in the figure by different numbers fordiopters (dpt) following the letters G, R, and B. Just as examples, thenumbers following each of these letters indicate diopters (1/m), orinverse distance of the depth plane from a viewer, and each box in thefigures represents an individual component color image. In someembodiments, to account for differences in the eye's focusing of lightof different wavelengths, the exact placement of the depth planes fordifferent component colors may vary. For example, different componentcolor images for a given depth plane may be placed on depth planescorresponding to different distances from the user. Such an arrangementmay increase visual acuity and user comfort and/or may decreasechromatic aberrations.

In some embodiments, light of each component color may be outputted by asingle dedicated waveguide and, consequently, each depth plane may havemultiple waveguides associated with it. In such embodiments, each box inthe figures including the letters G, R, or B may be understood torepresent an individual waveguide, and three waveguides may be providedper depth plane where three component color images are provided perdepth plane. While the waveguides associated with each depth plane areshown adjacent to one another in this drawing for ease of description,it will be appreciated that, in a physical device, the waveguides mayall be arranged in a stack with one waveguide per level. In some otherembodiments, multiple component colors may be outputted by the samewaveguide, such that, e.g., only a single waveguide may be provided perdepth plane.

With continued reference to FIG. 8, in some embodiments, G is the colorgreen, R is the color red, and B is the color blue. In some otherembodiments, other colors associated with other wavelengths of light,including magenta and cyan, may be used in addition to or may replaceone or more of red, green, or blue. In some embodiments, features 198,196, 194, and 192 may be active or passive optical filters configured toblock or selectively light from the ambient environment to the viewer'seyes.

It will be appreciated that references to a given color of lightthroughout this disclosure will be understood to encompass light of oneor more wavelengths within a range of wavelengths of light that areperceived by a viewer as being of that given color. For example, redlight may include light of one or more wavelengths in the range of about620-780 nm, green light may include light of one or more wavelengths inthe range of about 492-577 nm, and blue light may include light of oneor more wavelengths in the range of about 435-493 nm.

In some embodiments, the light source 2040 (FIG. 6) may be configured toemit light of one or more wavelengths outside the visual perceptionrange of the viewer, for example, infrared and/or ultravioletwavelengths. In addition, the incoupling, outcoupling, and other lightredirecting structures of the waveguides of the display 1000 may beconfigured to direct and emit this light out of the display towards theuser's eye 4, e.g., for imaging and/or user stimulation applications.

With reference now to FIG. 9A, in some embodiments, light impinging on awaveguide may need to be redirected to incouple that light into thewaveguide. An incoupling optical element may be used to redirect andincouple the light into its corresponding waveguide. FIG. 9A illustratesa cross-sectional side view of an example of a plurality or set 1200 ofstacked waveguides that each includes an incoupling optical element. Thewaveguides may each be configured to output light of one or moredifferent wavelengths, or one or more different ranges of wavelengths.It will be appreciated that the stack 1200 may correspond to the stack1178 (FIG. 6) and the illustrated waveguides of the stack 1200 maycorrespond to part of the plurality of waveguides 1182, 1184, 1186,1188, 1190, except that light from one or more of the image injectiondevices 1200, 1202, 1204, 1206, 1208 is injected into the waveguidesfrom a position that requires light to be redirected for incoupling.

The illustrated set 1200 of stacked waveguides includes waveguides 1210,1220, and 1230. Each waveguide includes an associated incoupling opticalelement (which may also be referred to as a light input area on thewaveguide), with, e.g., incoupling optical element 1212 disposed on amajor surface (e.g., an upper major surface) of waveguide 1210,incoupling optical element 1224 disposed on a major surface (e.g., anupper major surface) of waveguide 1220, and incoupling optical element1232 disposed on a major surface (e.g., an upper major surface) ofwaveguide 1230. In some embodiments, one or more of the incouplingoptical elements 1212, 1222, 1232 may be disposed on the bottom majorsurface of the respective waveguide 1210, 1220, 1230 (particularly wherethe one or more incoupling optical elements are reflective, deflectingoptical elements). As illustrated, the incoupling optical elements 1212,1222, 1232 may be disposed on the upper major surface of theirrespective waveguide 1210, 1220, 1230 (or the top of the next lowerwaveguide), particularly where those incoupling optical elements aretransmissive, deflecting optical elements. In some embodiments, theincoupling optical elements 1212, 1222, 1232 may be disposed in the bodyof the respective waveguide 1210, 1220, 1230. In some embodiments, asdiscussed herein, the incoupling optical elements 1212, 1222, 1232 arewavelength selective, such that they selectively redirect one or morewavelengths of light, while transmitting other wavelengths of light.While illustrated on one side or corner of their respective waveguide1210, 1220, 1230, it will be appreciated that the incoupling opticalelements 1212, 1222, 1232 may be disposed in other areas of theirrespective waveguide 1210, 1220, 1230 in some embodiments.

As illustrated, the incoupling optical elements 1212, 1222, 1232 may belaterally offset from one another. In some embodiments, each incouplingoptical element may be offset such that it receives light without thatlight passing through another incoupling optical element. For example,each incoupling optical element 1212, 1222, 1232 may be configured toreceive light from a different image injection device 1200, 1202, 1204,1206, and 1208 as shown in FIG. 6, and may be separated (e.g., laterallyspaced apart) from other incoupling optical elements 1212, 1222, 1232such that it substantially does not receive light from the other ones ofthe incoupling optical elements 1212, 1222, 1232.

Each waveguide also includes associated light distributing elements,with, e.g., light distributing elements 1214 disposed on a major surface(e.g., a top major surface) of waveguide 1210, light distributingelements 1224 disposed on a major surface (e.g., a top major surface) ofwaveguide 1220, and light distributing elements 1234 disposed on a majorsurface (e.g., a top major surface) of waveguide 1230. In some otherembodiments, the light distributing elements 1214, 1224, 1234, may bedisposed on a bottom major surface of associated waveguides 1210, 1220,1230, respectively. In some other embodiments, the light distributingelements 1214, 1224, 1234, may be disposed on both top and bottom majorsurface of associated waveguides 1210, 1220, 1230, respectively; or thelight distributing elements 1214, 1224, 1234, may be disposed ondifferent ones of the top and bottom major surfaces in differentassociated waveguides 1210, 1220, 1230, respectively.

The waveguides 1210, 1220, 1230 may be spaced apart and separated by,e.g., gas, liquid, and/or solid layers of material. For example, asillustrated, layer 1218 a may separate waveguides 1210 and 1220; andlayer 1218 b may separate waveguides 1220 and 1230. In some embodiments,the layers 1218 a and 1218 b are formed of low refractive indexmaterials (that is, materials having a lower refractive index than thematerial forming the immediately adjacent one of waveguides 1210, 1220,1230). Preferably, the refractive index of the material forming thelayers 1218 a, 1218 b is 0.05 or more, or 0.10 or more less than therefractive index of the material forming the waveguides 1210, 1220,1230. Advantageously, the lower refractive index layers 1218 a, 1218 bmay function as cladding layers that facilitate total internalreflection (TIR) of light through the waveguides 1210, 1220, 1230 (e.g.,TIR between the top and bottom major surfaces of each waveguide). Insome embodiments, the layers 1218 a, 1218 b are formed of air. While notillustrated, it will be appreciated that the top and bottom of theillustrated set 1200 of waveguides may include immediately neighboringcladding layers.

Preferably, for ease of manufacturing and other considerations, thematerial forming the waveguides 1210, 1220, 1230 are similar or thesame, and the material forming the layers 1218 a, 1218 b are similar orthe same. In some embodiments, the material forming the waveguides 1210,1220, 1230 may be different between one or more waveguides, and/or thematerial forming the layers 1218 a, 1218 b may be different, while stillholding to the various refractive index relationships noted above.

With continued reference to FIG. 9A, light rays 1240, 1242, 1244 areincident on the set 1200 of waveguides. It will be appreciated that thelight rays 1240, 1242, 1244 may be injected into the waveguides 1210,1220, 1230 by one or more image injection devices 1200, 1202, 1204,1206, 1208 (FIG. 6).

In some embodiments, the light rays 1240, 1242, 1244 have differentproperties, e.g., different wavelengths or different ranges ofwavelengths, which may correspond to different colors. The incouplingoptical elements 1212, 122, 1232 each deflect the incident light suchthat the light propagates through a respective one of the waveguides1210, 1220, 1230 by TIR.

For example, incoupling optical element 1212 may be configured todeflect ray 1240, which has a first wavelength or range of wavelengths.Similarly, the transmitted ray 1242 impinges on and is deflected by theincoupling optical element 1222, which is configured to deflect light ofa second wavelength or range of wavelengths. Likewise, the ray 1244 isdeflected by the incoupling optical element 1232, which is configured toselectively deflect light of third wavelength or range of wavelengths.

With continued reference to FIG. 9A, the deflected light rays 1240,1242, 1244 are deflected so that they propagate through a correspondingwaveguide 1210, 1220, 1230; that is, the incoupling optical elements1212, 1222, 1232 of each waveguide deflects light into thatcorresponding waveguide 1210, 1220, 1230 to incouple light into thatcorresponding waveguide. The light rays 1240, 1242, 1244 are deflectedat angles that cause the light to propagate through the respectivewaveguide 1210, 1220, 1230 by TIR. The light rays 1240, 1242, 1244propagate through the respective waveguide 1210, 1220, 1230 by TIR untilimpinging on the waveguide's corresponding light distributing elements1214, 1224, 1234.

With reference now to FIG. 9B, a perspective view of an example of theplurality of stacked waveguides of FIG. 9A is illustrated. As notedabove, the incoupled light rays 1240, 1242, 1244, are deflected by theincoupling optical elements 1212, 1222, 1232, respectively, and thenpropagate by TIR within the waveguides 1210, 1220, 1230, respectively.The light rays 1240, 1242, 1244 then impinge on the light distributingelements 1214, 1224, 1234, respectively. The light distributing elements1214, 1224, 1234 deflect the light rays 1240, 1242, 1244 so that theypropagate towards the outcoupling optical elements 1250, 1252, 1254,respectively.

In some embodiments, the light distributing elements 1214, 1224, 1234are orthogonal pupil expanders (OPE's). In some embodiments, the OPE'sboth deflect or distribute light to the outcoupling optical elements1250, 1252, 1254 and also increase the beam or spot size of this lightas it propagates to the outcoupling optical elements. In someembodiments, e.g., where the beam size is already of a desired size, thelight distributing elements 1214, 1224, 1234 may be omitted and theincoupling optical elements 1212, 1222, 1232 may be configured todeflect light directly to the outcoupling optical elements 1250, 1252,1254. For example, with reference to FIG. 9A, the light distributingelements 1214, 1224, 1234 may be replaced with outcoupling opticalelements 1250, 1252, 1254, respectively. In some embodiments, theoutcoupling optical elements 1250, 1252, 1254 are exit pupils (EP's) orexit pupil expanders (EPE's) that direct light in a viewer's eye 4 (FIG.7).

Accordingly, with reference to FIGS. 9A and 9B, in some embodiments, theset 1200 of waveguides includes waveguides 1210, 1220, 1230; incouplingoptical elements 1212, 1222, 1232; light distributing elements (e.g.,OPE's) 1214, 1224, 1234; and outcoupling optical elements (e.g., EP's)1250, 1252, 1254 for each component color. The waveguides 1210, 1220,1230 may be stacked with an air gap/cladding layer between each one. Theincoupling optical elements 1212, 1222, 1232 redirect or deflectincident light (with different incoupling optical elements receivinglight of different wavelengths) into its waveguide. The light thenpropagates at an angle which will result in TIR within the respectivewaveguide 1210, 1220, 1230. In the example shown, light ray 1240 (e.g.,blue light) is deflected by the first incoupling optical element 1212,and then continues to bounce down the waveguide, interacting with thelight distributing element (e.g., OPE's) 1214 and then the outcouplingoptical element (e.g., EPs) 1250, in a manner described earlier. Thelight rays 1242 and 1244 (e.g., green and red light, respectively) willpass through the waveguide 1210, with light ray 1242 impinging on andbeing deflected by incoupling optical element 1222. The light ray 1242then bounces down the waveguide 1220 via TIR, proceeding on to its lightdistributing element (e.g., OPEs) 1224 and then the outcoupling opticalelement (e.g., EP's) 1252. Finally, light ray 1244 (e.g., red light)passes through the waveguide 1220 to impinge on the light incouplingoptical elements 1232 of the waveguide 1230. The light incouplingoptical elements 1232 deflect the light ray 1244 such that the light raypropagates to light distributing element (e.g., OPEs) 1234 by TIR, andthen to the outcoupling optical element (e.g., EPs) 1254 by TIR. Theoutcoupling optical element 1254 then finally outcouples the light ray1244 to the viewer, who also receives the outcoupled light from theother waveguides 1210, 1220.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B. As illustrated, the waveguides1210, 1220, 1230, along with each waveguide's associated lightdistributing element 1214, 1224, 1234 and associated outcoupling opticalelement 1250, 1252, 1254, may be vertically aligned. However, asdiscussed herein, the incoupling optical elements 1212, 1222, 1232 arenot vertically aligned; rather, the incoupling optical elements arepreferably non-overlapping (e.g., laterally spaced apart as seen in thetop-down view). As discussed further herein, this nonoverlapping spatialarrangement facilitates the injection of light from different resourcesinto different waveguides on a one-to-one basis, thereby allowing aspecific light source to be uniquely coupled to a specific waveguide. Insome embodiments, arrangements including nonoverlappingspatially-separated incoupling optical elements may be referred to as ashifted pupil system, and the in coupling optical elements within thesearrangements may correspond to sub pupils.

Bragg-Reflective Structures Based on Liquid Crystals

Generally, liquid crystals possess physical properties that may beintermediate between conventional fluids and solids. While liquidcrystals are fluid-like in some aspects, unlike most fluids, thearrangement of molecules within liquid crystals exhibits some structuralorder. Different types of liquid crystals include thermotropic,lyotropic, and polymeric liquid crystals. Thermotropic liquid crystalsdisclosed herein can be implemented in various physical states, e.g.,phases, including a nematic state/phase, a smectic state/phase, a chiralnematic state/phase or a chiral smectic state/phase.

As described herein, liquid crystals in a nematic state or phase canhave calamitic (rod-shaped) or discotic (disc-shaped) organic moleculesthat have relatively little positional order, while having a long-rangedirectional order with their long axes being roughly parallel. Thus, theorganic molecules may be free to flow with their center of masspositions being randomly distributed as in a liquid, while stillmaintaining their long-range directional order. In some implementations,liquid crystals in a nematic phase can be uniaxial; i.e., the liquidcrystals have one axis that is longer and preferred, with the other twobeing roughly equivalent. In other implementations, liquid crystals canbe biaxial; i.e., in addition to orienting their long axis, the liquidcrystals may also orient along a secondary axis.

As described herein, liquid crystals in a smectic state or phase canhave the organic molecules that form relatively well-defined layers thatcan slide over one another. In some implementations, liquid crystals ina smectic phase can be positionally ordered along one direction. In someimplementations, the long axes of the molecules can be oriented along adirection substantially normal to the plane of the liquid crystal layer,while in other implementations, the long axes of the molecules may betilted with respect to the direction normal to the plane of the layer.

Herein and throughout the disclosure, nematic liquid crystals arecomposed of rod-like molecules with the long axes of neighboringmolecules approximately aligned to one another. To describe thisanisotropic structure, a dimensionless unit vector n called thedirector, may be used to describe the direction of preferred orientationof the liquid crystal molecules.

Herein and throughout the disclosure, a tilt angle or a pre-tilt angle(can refer to an angle measured in a plane perpendicular to a majorsurface (in an x-y plane) of the liquid crystal layers or of thesubstrate, e.g., the x-z plane, and measured between an alignmentdirection and the major surface or a direction parallel to the majorsurface, e.g., the x-direction.

Herein and throughout the disclosure, an azimuthal angle or a rotationangle φ is used to describe an angle of rotation about a layer normaldirection, or an axis normal to a major surface of a liquid crystallayer, which is measured in a plane parallel to a major surface of theliquid crystal layers or of the substrate, e.g., the x-y plane, andmeasured between an alignment direction, e.g., an elongation directionor the direction of the director, and a direction parallel to the majorsurface, e.g., the y-direction.

Herein and throughout the disclosure, when an angle such as the rotationangle φ or a pre-tilt angle Φ are referred to as being substantially thesame between different regions, it will be understood that an averagealignment angles can, for example, be within about 1%, about 5% or about10% of each other although the average alignment can be larger in somecases.

Herein and throughout the specification, a duty cycle can, for example,refers to a ratio between a first lateral dimension of a first regionhaving liquid crystal molecules aligned in a first alignment direction,and the grating period of the zone having the first region. Whereapplicable, the first region corresponds to the region in which thealignment of the liquid crystals does not vary between different zones.

As describe herein, liquid crystals in a nematic state or a smecticstate can also exhibit chirality. Such liquid crystals are referred toas being in a chiral phase or a cholesteric phase. In a chiral phase ora cholesteric phase, the liquid crystals can exhibit a twisting of themolecules perpendicular to the director, with the molecular axisparallel to the director. The finite twist angle between adjacentmolecules is due to their asymmetric packing, which results inlonger-range chiral order.

As described herein, liquid crystals in a chiral smectic state or phasecan be configured such that the liquid crystal molecules have positionalordering in a layered structure, with the molecules tilted by a finiteangle with respect to the layer normal. In addition, chirality caninduce successive azimuthal twists of the liquid crystal molecules withrespect to a direction perpendicular to the layer normal from one liquidcrystal molecule to the next liquid crystal molecule in the layer normaldirection, thereby producing a spiral twisting of the molecular axisalong the layer normal.

As described herein and throughout the disclosure, a chiral structurerefers to a plurality of liquid crystal molecules in a cholesteric phasethat extend in a direction, e.g., a direction perpendicular to thedirector such as a layer depth direction, and are successively rotatedor twisted in a rotation direction, e.g., clockwise or counterclockwise.In one aspect, the directors of the liquid crystal molecules in a chiralstructure can be characterized as a helix having a helical pitch.

As described herein, liquid crystals in a cholesteric phase displayingchirality can be described as having a chiral pitch, or a helical pitch(p), which corresponds to a length in the layer depth directioncorresponding to a net rotation angle of the liquid crystal molecules ofthe chiral structures by one full rotation in the first rotationdirection. In other words, the helical pitch refers to the distance overwhich the liquid crystal molecules undergo a full 3600 twist. Thehelical pitch (p) can change, e.g., when the temperature is altered orwhen other molecules are added to a liquid crystal host (an achiralliquid host material can form a chiral phase if doped with a chiralmaterial), allowing the helical pitch (p) of a given material to betuned accordingly. In some liquid crystal systems, the helical pitch isof the same order as the wavelength of visible light. As describedherein, liquid crystals displaying chirality can also be described ashaving a twist angle, or a rotation angle (0), which can refer to, forexample, the relative azimuthal angular rotation between successiveliquid crystal molecules in the layer normal direction, and as having anet twist angle, or a net rotation angle, which can refer to, forexample, the relative azimuthal angular rotation between an uppermostliquid crystal molecule and a lowermost liquid crystal molecule across aspecified length, e.g., the length of a chiral structure or thethickness of the liquid crystal layer.

According to various embodiments described herein, liquid crystalshaving various states or phases as described above can be configured tooffer various desirable material properties, including, e.g.,birefringence, optical anisotropy, and manufacturability using thin-filmprocesses. For example, by changing surface conditions of liquid crystallayers and/or mixing different liquid crystal materials, gratingstructures that exhibit spatially varying diffraction properties, e.g.,gradient diffraction efficiencies, can be fabricated.

As described herein, “polymerizable liquid crystals” may refer to liquidcrystal materials that can be polymerized, e.g., in-situphotopolymerized, and may also be described herein as reactive mesogens(RM).

It will be appreciated that the liquid crystal molecules may bepolymerizable in some embodiments and, once polymerized, may form alarge network with other liquid crystal molecules. For example, theliquid crystal molecules may be linked by chemical bonds or linkingchemical species to other liquid crystal molecules. Once joinedtogether, the liquid crystal molecules may form liquid crystal domainshaving substantially the same orientations and locations as before beinglinked together. For ease of description, the term “liquid crystalmolecule” is used herein to refer to both the liquid crystal moleculesbefore polymerization and to the liquid crystal domains formed by thesemolecules after polymerization.

According to particular embodiments described herein,photo-polymerizable liquid crystal materials can be configured to formBragg-reflective structures, e.g., a diffraction grating, whose materialproperties, including birefringence, chirality, and ease formultiple-coating, can be utilized to create diffraction gratings withdifferent material properties, e.g., birefringence, chirality, andthickness, which can result in different optical properties, e.g.,diffraction efficiency, wavelength selectivity and off-axis diffractionangle selectivity, to name a few.

It will be appreciated that, as described herein, a “transmissive” or“transparent” structure, e.g., a transparent substrate, may allow atleast some, e.g., at least 20, 30 or 50%, of an incident light, to passtherethrough. Accordingly, a transparent substrate may be a glass,sapphire or a polymeric substrate in some embodiments. In contrast, a“reflective” structure, e.g., a reflective substrate, may reflect atleast some, e.g., at least 20, 30, 50, 70, 90% or more of the incidentlight, to reflect therefrom.

Optical properties of a grating are determined by the physicalstructures of the grating (e.g., the periodicity, the depth, and theduty cycle), as well as material properties of the grating (e.g.,refractive index, absorption, and birefringence). When liquid crystalsare used, optical properties of the grating can be controlled bycontrolling, e.g., molecular orientation or distribution of the liquidcrystal materials. For example, by varying molecular orientation ordistribution of the liquid crystal material across the grating area, thegrating may exhibit graded diffraction efficiencies. Such approaches aredescribed in the following, in reference to the figures.

Cholesteric Liquid Crystal Diffraction Grating (CLCG)

As described supra in reference to FIGS. 6 and 7, display systemsaccording to various embodiments described herein may include opticalelements, e.g., incoupling optical elements, outcoupling opticalelements, and light distributing elements, which may include diffractiongratings. For example, as described above in reference to FIG. 7, light400 that is injected into the waveguide 1182 at the input surface 1382of the waveguide 1182 propagates within the waveguide 1182 by totalinternal reflection (TIR). At points where the light 400 impinges on theout-coupling optical element 1282, a portion of the light exits thewaveguide as exit beams 402. In some implementations, any of the opticalelements 1182, 1282, or 1382 can be configured as a diffraction grating.

Efficient light in-coupling into (or out-coupling from) the waveguide1182 can be a challenge in designing a waveguide-based see-throughdisplays, e.g., for virtual/augmented/mixed display applications. Forthese and other applications, it is desirable to have the diffractiongrating formed of a material whose structure is configurable to optimizevarious optical properties, including diffraction properties. Thedesirable diffraction properties include, among other properties,polarization selectivity, spectral selectivity, angular selectivity,high spectral bandwidth and high diffraction efficiencies, among otherproperties. To address these and other needs, in various embodimentsdisclosed herein, the optical element 1282 is configured as acholesteric liquid crystal diffraction grating (CLCG). As describedinfra, CLCGs according to various embodiments can be configured tooptimize, among other things, polarization selectivity, bandwidth, phaseprofile, spatial variation of diffraction properties, spectralselectivity and high diffraction efficiencies.

In the following, various embodiments of CLCGs configured as areflective liquid crystal diffraction grating comprising cholestericliquid crystals (CLC) optimized for various optical properties aredescribed. Generally, diffraction gratings have a periodic structure,which splits and diffracts light into several beams travelling indifferent directions. The directions of these beams depend, among otherthings, on the period of the periodic structure and the wavelength ofthe light. To optimize certain optical properties, e.g., diffractionefficiencies, for certain applications such as outcoupling opticalelement 1282 (FIGS. 6, 7), various material properties of the CLC can beoptimized as described infra.

As described supra, liquid crystal molecules of a cholesteric liquidcrystal (CLC) layer in a chiral (nematic) phase or a cholesteric phaseis characterized by a plurality of liquid crystal molecules that arearranged to have successive azimuthal twists of the director as afunction of position in the film in a normal direction, or a depthdirection, of the liquid crystal layer. As described herein, the liquidcrystal molecules that arranged to have the successive azimuthal twistsare collectively referred to herein as a chiral structure. As describedherein, an angle (ϕ) of azimuthal twist or rotation is described as theangle between the directors the liquid crystal molecules, as describedsupra, relative to a direction parallel to the layer normal. Thespatially varying director of the liquid crystal molecules of a chiralstructure can be described as forming a helical pattern in which thehelical pitch (p) is defined as the distance (e.g., in the layer normaldirection of the liquid crystal layer) over which the director hasrotated by 360°, as described above. As described herein, a CLC layerconfigured as a diffraction grating has a lateral dimension by which themolecular structures of the liquid crystals periodically repeat in alateral direction normal to the depth direction. This periodicity in thelateral direction is referred to as a grating period (A).

According to various embodiments described herein, a diffraction gratingcomprises a cholesteric liquid crystal (CLC) layer comprising aplurality of chiral structures, wherein each chiral structure comprisesa plurality of liquid crystal molecules that extend in a layer depthdirection by at least a helical pitch and are successively rotated in afirst rotation direction. The helical pitch is a length in the layerdepth direction corresponding to a net rotation angle of the liquidcrystal molecules of the chiral structures by one full rotation in thefirst rotation direction. The arrangements of the liquid crystalmolecules of the chiral structures vary periodically in a lateraldirection perpendicular to the layer depth direction

FIG. 10 illustrates a cross-sectional side view of a cholesteric liquidcrystal (CLC) layer 1004 comprising a plurality of uniform chiralstructures. The CLC 1004 comprises a CLC layer 1008 comprising liquidcrystal molecules arranged as a plurality of chiral structures 1012-1,1012-2, . . . 1012-i, wherein each chiral structure comprises aplurality of liquid crystal molecules, where is any suitable integergreater than 2. For example, the chiral structure 1012-1 comprises aplurality of liquid crystal molecules 1012-1-1, 1012-1-2, . . . 1012-1-jthat are arranged to extend in a layer normal direction, e.g., thez-direction in the illustrated embodiment, where j is any suitableinteger greater than 2. The liquid crystal molecules of each chiralstructure are successively rotated in a first rotation direction. In theillustrated embodiment, the liquid crystal molecules are successivelyrotated in a clockwise direction when viewing in a positive direction ofthe z-axis (e.g., the direction of the axis arrow), or the direction ofpropagation of the incident light beams 1016-L, 1016-R. For example, inthe illustrated embodiment, the liquid crystal molecules 1012-1-1,1012-1-2, . . . 1012-1-j of the chiral structure 1012-1 are successivelyrotated by rotation angles ϕ₁, ϕ₂, . . . ϕ_(j), relative to, e.g., thepositive x-direction. In the illustrated embodiment, for illustrativepurposes, the plurality of liquid crystal molecules of each of thechiral structures 1012-1, 1012-2, . . . 1012-i between opposing ends inthe z-direction are rotated by one full rotation or turn, such that thenet rotation angle of the liquid crystal molecules is about 360°. As aresult, the chiral structures 1012-1, 1012-2, . . . 1012-i have a lengthL in the z-direction that is the same as the helical pitch p. However,embodiments are not so limited, and the chiral structures 1012-1,1012-2, . . . 1012-i can have any number of full rotations greater thanor less than 1, any suitable net rotation angle that is lower or higherthan 360°, and/or any suitable length L in the z-direction that isshorter or longer than the helical pitch p. For example, in variousembodiments described herein, the number of full turns of the chiralstructures can be between 1 and 3, between 2 and 4, between 3 and 5,between 4 and 6, between 5 and 7, between 6 and 8, between 7 and 9, orbetween 8 and 10, among other numbers.

Still referring to FIG. 10, the successive rotation angles betweenadjacent liquid crystal molecules in the z-direction, ϕ₁, ϕ₂, . . .ϕ_(j), can be the same according to some embodiments, or be differentaccording to some other embodiments. By way of illustration, in theillustrated embodiment, the length of the chiral structures 1012-1,1012-2, . . . 1012-i is about p and the net rotation angle is 360°, suchthat adjacent liquid crystal molecules in the z-direction are rotated byabout 360°/(m−1), where m is the number of liquid crystal molecules in achiral structure. For example, for illustrative purposes, each of thechiral structure 1012-1, 1012-2, . . . 1012-i has 13 liquid crystalmolecules, such that adjacent liquid crystal molecules in thez-direction are rotated with respect to each other by about 30°. Ofcourse, chiral structures in various embodiments can have any suitablenumber of liquid crystal molecules.

Thus, still referring to FIG. 10, the chiral structures that areadjacent in a lateral direction, e.g., x-direction, have similarlyarranged liquid crystal molecules. In the illustrated embodiment, thechiral structures 1012-1, 1012-2, . . . 1012-i are similarly configuredsuch that liquid crystal molecules of the different chiral structuresthat are at about the same depth, e.g., the liquid crystal moleculesclosest to the light-incident surface 1004S, have the same rotationangle, as well as successive rotation angles of successive liquidcrystal molecules at about the same depth, as well as the net rotationangle of the liquid crystal molecules of each chiral structure.

In the following, the CLC layer 1004 illustrated in FIG. 10 is furtherdescribed in operation. As described, the CLC layer 1004 comprises thechiral structures 1012-1, 1012-2, . . . 1012-i having a uniformarrangement in a lateral direction, e.g., x-direction. In operation,when incident light having a combination of light beams havingleft-handed circular polarization and light beams having right-handedcircular polarization are incident on the surface 1004S of the CLC layer1008, by Bragg-reflection, light with one of the circular polarizationhandedness is reflected by the CLC layer 1004, while light with theopposite polarization handedness is transmitted through the CLC layer1008 without substantial interference. As described herein andthroughout the disclosure, the handedness is defined as viewed in thedirection of propagation. According to embodiments, when the directionof polarization, or handedness of the polarization, of the light beams1016-L, 1016-R is matched such that it and has the same direction ofrotation as the liquid crystal molecules of the chiral structures1012-1, 1012-2, . . . 1012-i, the incident light is reflected. Asillustrated, incident on the surface 1004S are light beams 1016-L havingleft-handed circular polarization and light beams 1016-R having aright-handed circular polarization. In the illustrated embodiment, theliquid crystal molecules of the chiral structures 1012-1, 1012-2, . . .1012-i are rotated in a clockwise direction successively in thedirection in which incident light beams 1016-L, 1016-R travel, i.e.,positive x-direction, which is the same rotation direction as the lightteams 1016-R having right-handed circular polarization. As a result, thelight beams 1016-R having right-handed circular polarization aresubstantially reflected, whereas the light beams 1016-L havingleft-handed circular polarization are substantially transmitted throughthe CLC layer 1004.

Without being bound to any theory, under a Bragg-reflection condition,the wavelength of the incident light (λ) may be proportional to the meanor average refractive index (n) of a CLC layer and to the helical pitch(p), and can be expressed as satisfying the following condition undersome circumstances:λ≈np  [1]

In addition, the bandwidth (Δλ) of Bragg-reflecting wavelengths may beproportional to the birefringence Δn (e.g., the difference in refractiveindex between different polarizations of light) of CLC layer 1004 and tothe helical pitch (p), and can be expressed as satisfying the followingcondition under some circumstances:Δλ=Δn·p  [2]

In various embodiments described herein, the bandwidth Δλ is about 60nm, about 80 nm or about 100 nm.

According to various embodiments, a peak reflected intensity within avisible wavelength range between, e.g., about 390 nm and about 700 nm,or within a near infrared wavelength range between, e.g., about 700 nmand about 2500 nm, can exceed about 60%, about 70%, about 80% or about90%. In addition, according to various embodiments, the full width athalf maximum (FWHM) can be less than about 100 nm, less than about 70nm, less than about 50 nm or less than about 20 nm.

FIG. 11 illustrates a cross-sectional side view of a CLC grating (CLCG)1150 having differently arranged chiral structures in a lateraldirection, e.g., varying twist angles in a lateral direction. Similar tothe CLC layer 1004 of FIG. 10, the diffraction grating 1150 comprises acholesteric liquid crystal (CLC) layer 1158 comprising liquid crystalmolecules arranged as a plurality of chiral structures 1162-1, 1162-2, .. . 1162-i, wherein each chiral structure comprises a plurality ofliquid crystal molecules. For example, the chiral structure 1162-1comprises a plurality of liquid crystal molecules 1162-1-1, 1162-1-2, .. . 1162-1-j that are arranged to extend in a layer normal direction,represented as z-direction in the illustrated embodiment. The liquidcrystal molecules of each chiral structure are successively rotated in afirst rotation direction in a similar manner as described with respectto FIG. 10. In addition, various other parameters of the chiralstructures including the length L, the number of full rotations made bythe liquid crystal molecules and the number of liquid crystal moleculesper chiral structure are similar to the chiral structures describedabove with respect to FIG. 10.

In contrast to the illustrated embodiment of FIG. 10, however, in theillustrated embodiment of FIG. 11, the chiral structures that areadjacent in a lateral direction, e.g., x-direction, have differentlyarranged liquid crystal molecules. The chiral structures 1162-1, 1162-2,. . . 1162-i are differently configured in the x-direction such that theliquid crystal molecules of the different chiral structures at about thesame depth have different rotation angles. For example, in theillustrated embodiment, the liquid crystal molecules 1162-1-1, 1162-2-1,. . . 1162-i-1, that are closest to the incident surface 1158S, of thechiral structures 1162-1, 1162-2, . . . 1162-i, respectively, aresuccessively rotated by rotation angles ϕ₁, ϕ₂, . . . ϕ_(i) in thepositive x-axis direction relative to, e.g., positive x-direction. Inthe illustrated embodiment, the net rotation angle of the liquid crystalmolecules 1162-1-1, 1162-2-1, . . . 1162-i-1, that are closest to theincident surface 1158S across a lateral length A, which corresponds to aperiod of the diffraction grating 1150, is a rotation angle of about180°. In addition, liquid crystal molecules of different chiralstructures that are disposed at about the same depth level are rotatedby about the same rotation angle relative to respective surface-mostliquid crystal molecules.

Still referring to FIG. 11A, the successive rotation angles ϕ₁, ϕ₂, . .. ϕ_(i) of liquid crystal molecules that are at the same depth levelacross the period Λ in the x-direction can be the same according to someembodiments, or be different according to some other embodiments. In theillustrated embodiment, for the period Λ, when the net rotation angle is360° as in the illustrated embodiment, adjacent liquid crystal moleculesin the x-direction are rotated by about 360°/(m−1), where m is thenumber of liquid crystal molecules spanned by a period Λ in thex-direction. For example, for illustrative purposes, there are 7 liquidcrystal molecules that span across the period Λ, such that adjacentliquid crystal molecules at the same vertical level in the x-directionare rotated with respect to each other by about 30°. Of course, chiralstructures in various embodiments can have any suitable number of liquidcrystal molecules.

It will be appreciated that, for illustrating purposes, the CLC layer1158 is illustrated to have only one period Λ. Of course, embodimentsare not so limited, and the CLC layer 1158 can have any suitable numberof periods that is determined by the lateral dimension of the CLCG inthe x-direction.

As illustrated by the CLCG 1150, when the chiral structures in a lateraldirection, e.g., x-direction, are differently arranged, e.g.,successively rotated, the successively rotated chiral structures induceshifts in the relative phases of the reflected light along thex-direction. This is illustrated with respect to graph 1170, which plotsthe phase change ϕ resulting from the chiral structures that aresuccessively rotated by rotation angles ϕ₁, ϕ₂, . . . ϕ_(i) in thex-axis direction in one period Λ. Without being bound to any theory, therelative phase difference (Δϕ) of reflected light 1018 can be expressedas Δϕ(x)=(2πx/Λ), where x is the position along the lateral directionand Λ is the period. The bandwidth can be expressed as Δλ≈Δn·p.

Referring back to FIGS. 10-11 and Eqs. [1] and [2], according to variousembodiments, the Bragg-reflected wavelength can be varied by varying thehelical pitch p of the chiral structures. In various embodiments,without being bound to any theory, the helical pitch p can be varied byincreasing or decreasing helical twisting power (HTP), which refers tothe ability of a chiral compound to induce the rotation or twist anglesas described above. The HTP can in turn be varied by changing the amountof chiral compound relative to the amount of non-chiral compound. Invarious embodiments, by mixing a chiral compound chemically and/ormechanically with a non-chiral compound, e.g., a nematic compound, theBragg-reflection wavelength and thus the color can be varied based on aninverse relationship between the relative fraction of the chiralcompound and the helical pitch. In various embodiments disclosed herein,the ratio of the amount of chiral compound to the amount of nonchiralcompound can be about 20:1, 10:1, 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3,1:4, 1:5, 1:10 or about 1:20 by weight.

In the description supra with respect to FIGS. 10 and 11, the incidentlight beams 1016-L, 1016-R are illustrated as being propagating in adirection parallel to the layer normal, e.g., in the z-direction. Forvarious applications, however, e.g., as described above with respect toFIGS. 6 and 7, light propagating within the waveguide 1182, e.g.,propagating by total internal reflection (TIR), impinges on theoutcoupling optical elements 1282, 1284, 1286, 1288, 1290, e.g.,diffraction gratings, at an off-axis angle. The diffraction gratingsdescribed herein can be configured to maximize bandwidth and diffractionefficiency for such configurations, as described below.

In the description supra with respect to FIGS. 10 and 11, the liquidcrystal molecules are illustrated to not be pre-tilted. Embodiment arenot so limited, however, and the liquid crystal molecules can have apre-tilt angle D, relative to a direction parallel to a major surface ofthe CLCG, e.g., relative to the x-y plane that is between about +/−60degrees and about +/−90 degrees or between about +/−65 degrees and about+/−85 degrees, for instance about +/−75 degree; between about +/−35degrees and about +/−65 degrees or between about +/−40 degrees and about+/−60 degrees, for instance about +−50 degrees; between about +/−10degrees and about +/−40 degrees or between about +−15 degrees and about+/−35 degrees, for instance about +/−25 degrees, according to someembodiments. According to some other embodiments, the pre-tilt angle(can be between about ±15 degrees or between about ±10 degrees orbetween about ±5, e.g., 0 degrees.

CLCGs Configured for High Bandwidth Reflection at Off-Axis IncidentAngle

FIG. 12 illustrates a cross-sectional side view of a CLC layer 1158configured for high bandwidth of reflection at an off-axis incidentangle. As described herein, an off-axis incident angle refers an angleof incidence θ_(inc) of an incident beam 1216 with respect to thedirection of layer normal (e.g., z-direction in FIG. 12) that has anon-zero value, resulting in a Bragg-reflected beam 1220 at a reflectionangle θ. Under some circumstances, the reflection angle can be varied toa limited extent by varying a λ/Λ. Without being limited by any theory,under some circumstances, off-axis reflection can be described based onthe following relationship:n·sin(θ)=λ/Λ+sin(θ_(inc)),  [3]where θ_(inc) is the incident angle relative to the direction of layernormal, θ is the reflection angle relative to the direction of layernormal and n is a reflective index of a medium in which the reflectedbeam propagates. When the CLC layer 1158 is illuminated with theincident beam 1216 at an off-axis angle, the reflection spectrum may beshifted toward shorter wavelengths. According to various embodimentsdisclosed herein, the ratio VA can have a value between 0.5 and 0.8,between 0.6 and 0.9, between 0.7 and 1.0, between 0.8 and 1.1, between0.9 and 1.2, between 1.0 and 1.6, between 1.1 and 1.5, or between 1.2and 1.4.

Without being bound to any theory, the off-axis angle at which the CLClayer 1158 is configured to Bragg-reflect with high efficiency can alsodepend on the helical pitch p of the chiral structures.

FIGS. 13A and 13B illustrate cross-sectional side views of CLC layersconfigured for reflection at off-axis incident angles. Referring to FIG.13A, a first cholesteric liquid crystal (CLC) layer 1358A comprises afirst plurality of chiral structures having a first helical pitch (p₁).The first CLC layer 1358A has a first helical pitch p₁ such thatBragg-reflection is at a maximum when a first incident light beam 1316Ais directed to an incident surface of the CLC layer 1358A at a firstoff-axis angle θ_(inc,1), which results in a first reflected light beam1320A at a first reflection angle θ₁. As illustrated, the CLC layer1358A is further configured to have a first range 1324A of off-axisincident angles in which relatively high diffraction efficiency can beobtained. The first range 1324A can correspond to a range of off-axisincident angles outside of which the intensity of the first reflectedlight beam 1320A falls off by more than, e.g., 1/e. For example, thefirst range 1324A can have values of, θ_(inc,1)±3°, θ_(inc,1)±5°,θ_(inc,1)±7°, θ_(inc,1)±10° or θ_(inc,1)±20°.

Referring to FIG. 13B, a second cholesteric liquid crystal (CLC) layer1358B different from the first CLC layer 1358A comprising a secondplurality of chiral structures having a second helical pitch (p₂)different from the first helical pitch p₁ of the first CLC layer 1358Aof FIG. 13A.

As illustrated, the second CLC layer 1358B is configured such that whena second incident light beam 1316B is directed to an incident surface ofthe CLC layer 1358B at a second off-axis angle θ_(inc,2) different fromthe first off-axis angle θ_(inc1), a second reflected light beam 1320Bhaving a second reflection angle θ₂ different from the first reflectionangle θ₁ is generated As illustrated, the CLC layer 1358B is furtherconfigured to have a second range 1324B of off-axis angles, similar tothe first range 1324A described above with respect to FIG. 13A.

FIG. 13C illustrates a cross-sectional side view of a CLCG 1358including a plurality of CLC layers having different helical pitches ina stacked configuration for Bragg-reflection at a plurality of off-axisincident angles and high diffraction bandwidth. The CLCG 1358 includesCLC layers 1358A, 1358B described above with respect to FIGS. 13A and13B, respectively, that are formed over one another, e.g., in a stackedconfiguration and/or in contact with each other. Various parameters ofthe plurality of CLC layers 1358A, 1358B including the different helicalpitches can be improved or optimized such that the CLCG 1358 isconfigured for efficient reflection at a plurality of off-axis incidentangles and for high diffraction efficiency over a wider range ofoff-axis angles than can be obtained using only one CLC. For example, inthe illustrated embodiments, p₁ and p₂ can be selected such that theresulting first and second ranges 1324A and 1324B at least partiallyoverlap to provide high diffraction efficiency over a contiguous rangeof wavelength that includes the first and second ranges 1324A and 1324B.However, in other embodiments, p₁ and p₂ can be selected such that thefirst and second ranges 1324A and 1324B do not overlap.

In operation, the first and second CLC layers 1358A, 1358B are formedover one another such that when first and second incident light beams1316A, 1316B at first and second off-axis angles θ_(inc1), θ_(inc2), aredirected to an incident surface of the first CLC layer 1358A, the firstincident light beam 1316A is substantially reflected by the first CLClayer 1358A at a first reflection angle θ₁, while the second incidentlight beam 1358B substantially transmits through the first CLC layer1358A towards an incident surface of the second CLC layer 1358B, andsubstantially reflected by the second CLC layer 1358B at the secondreflection angle θ₂. It will be appreciated that, while not shown forclarity, the concepts described above can be extended to any suitablenumber of CLC layers.

As described herein and throughout the specification, a light beam that“substantially transmits” through a layer may refer to the light havingat least 20%, 30%, 50%, 70% or 90%, of an incident light intensityremaining as the light exits the layer. Similarly, a light beam that is“substantially reflected” by a layer may refer to the light having atleast 20, 30, 50%, 70% or 90%, of an incident light intensity remainingin the reflected light.

Still referring to FIG. 13C, in various embodiments, the liquid crystalmolecules of the first and second CLC layers 1358A, 1358B can includethe same chiral compound at different amounts, such that CLC layers1358A, 1358B have different helical twisting power (HTP), as describedsupra. For example, the second CLC layer 1358B may have a higherrelative amount of the same chiral compound compared to the first CLClayer 1358A. In some embodiments, the pitch p may be inverselyproportional to the fraction of the chiral compound relative to thetotal liquid crystal compound which includes chiral and nonchiralcompounds. However, embodiments are not so limited, and the first andsecond CLC layers 1358A, 1358B can have different chiral compounds.

In addition, in various embodiments, the liquid crystal molecules of thefirst and second CLC layers 1358A, 1358B can include the same ordifferent chiral compounds, such that the CLC layers 1358A, 1358B havedifferent ratios λ/Λ₁ and λ/Λ₂, respectively, such that the CLC layers1358A, 1358B can be configured for high diffraction efficiencies atdifferent incident angles θ_(inc1), θ_(inc2), e.g., according to Eq.[3].

Still referring to FIG. 13C, first and second CLC layers 1358A, 1358Bcan be fabricated directly on the top of each other, according to someembodiments. For example, the first CLC layer 1358A can be deposited onan alignment layer that provides alignment conditions for the first CLClayer 1358A and subsequently, the second CLC layer 1358B can bedeposited on the first CLC layer 1358B. Under these fabricationconditions, the surface of the first CLC layer 1358A can providealignment conditions for the second CLC layer 1358B. In some otherembodiments, each of the CLC layers 1358A, 1358B can be fabricated withseparate alignment layers. For example, the first CLC layer 1358A can beformed on a first alignment layer and, a second alignment layer can beformed on the first CLC layer 1358A, and the second CLC layer 1358B onthe second alignment layer. An isolation layer, e.g., a thin oxidelayer, may be formed on the first CLC layer 1358A, according to someembodiments, prior to forming the second alignment layer and/or thesecond CLC layer 1358B. In yet other embodiments, the two CLC layers1358A, 1358B can be fabricated individually on different substrates andsubsequently stacked. In various embodiments, an intermediate layer canbe formed between the two CLC layers 1358A, 1358B, e.g., to enhanceadhesion.

The concepts described above with respect to CLCGs having a plurality ofCLC layers optimized for optimum diffraction efficiency at differentoff-axis angles can be extended to other alternative embodiments. Inparticular, in some embodiments, instead of forming a plurality oflayers, a single CLC layer can be configured to have different regionsthat are optimized for optimum diffraction efficiency at differentoff-axis angles.

FIG. 14 illustrates a cross-sectional side view of a CLCG 1400 includinga single CLC layer 1404 having vertical regions with different helicalpitches along a depth direction for Bragg-reflection at a plurality ofoff-axis incident angles at different vertical regions with highdiffraction bandwidth. The CLC layer 1404 has a plurality of verticalregions having different parameters, e.g., different helical pitches,that are optimized such that high diffraction efficiency can be obtainedover a wider range of off-axis angles than can be obtained using onlyone CLC layer having a uniform pitch in the depth direction. In theillustrated embodiment, the single CLC layer 1404 includes a pluralityof vertical regions 1404A, 1404B, 1404C and 1404D, which can havedifferent helical pitches p₁, p₂, p₃ and p₄, respectively. Similar to asdescribed above with respect to FIG. 13C, the helical pitches p₁, p₂, p₃and p₄ can be selected such that the plurality of vertical regions1404A, 1404B, 1404C and 1404D are configured for optimum diffractionefficiency at incident angles θ_(incA), θ_(incB), θ_(incC) and θ_(incD),respectively, which results in reflected light beams at differentvertical depths at corresponding reflection angles θ_(A), θ_(B), θ_(C),and θ_(D), respectively. Furthermore, as described above with respect toFIG. 13C, the CLC layer 1404 is further configured to have respectiveranges of off-axis angles in which relatively high diffractionefficiency can be obtained. Of course, while four vertical regions areillustrated for clarity, any suitable number of regions can be includedin the CLC layer 1404. In addition, different variations described abovewith respect to the CLCG 1358 of FIG. 13C having a plurality of CLClayers can be applicable to the CLCG 1400.

In the illustrated embodiment of FIG. 14, the values of the helicalpitches p1, p2, p3 and p4 decrease with increasing depth from anincident surface 1404S, such that a decreasing gradient in helical pitchis created in the depth direction (negative z-direction). When the rateof decrease of the helical pitch as a function of layer depth in thez-direction is uniform across the thickness of the CLC layer 1404, agraph 1408 representing a linear relationship between the depth and thehelical pitch can be obtained. However, embodiments are not so limited.For example, the helical pitches p₁, p₂, p₃ and p₄ can increase ordecrease at any depth and can change at different rates as a function oflayer depth, according to some other embodiments.

The CLC layer 1404 having a gradient in helical pitch can be fabricated,by varying, e.g., increasing or decreasing, the helical twisting power(HTP) of the liquid crystal molecules at different depths of the CLClayer. The HTP can in turn be spatially varied by changing the relativeamount of chiral compound. In various embodiments, by mixing a chiralcompound chemically and/or mechanically with a non-chiral compound,e.g., a nematic compound, at different vertical depths, the helicalpitches of the vertical regions 1404A, 1404B, 1404C and 1404D can beconfigured for optimum diffraction efficiency at different incidentangles θ_(incA), θ_(incB), θ_(incC) and θ_(incD), respectively, based onan inverse relationship between the relative fraction of the chiralcompound and the helical pitch. For example, a mixture of differentchemical components (e.g., chiral di-acrylate monomers andnematic/non-chiral mono-acrylate monomers) that undergo polymerizationprocess at different reaction rates under UV irradiation can be used.Additionally or alternatively, the HTP can be spatially varied bychanging irradiation conditions, including exposure intensity and/orexposure time, of UV irradiation at different depths of the CLC layer.The HTP can also be spatially varied by varying the pre-/post-processingof UV polymerization process including thermal treatments before, afterand/or during UV irradiation. For example, when a UV absorbing dye isadded to a mixture, an intensity gradient of the UV light at differentdepth of the CLC layer can be created. For example, due to the UVintensity gradient, the polymerization near the surface may proceed at afaster rate compared to the bottom region of the CLC layer. For example,when the cholesteric component is a di-acrylate, the probability ofbeing incorporated into the resulting polymer can be much higher, e.g.,twice as high, as the probability of nematic mono-acrylate beingincorporated in the polymer. Under some circumstances, if the overallpolymerization rate is controlled such that a depletion of the chiraldiacrylate near surface region of the CLC layer generates a di-acrylateconcentration gradient in the depth direction of the CLC layer. This inturn starts diffusion of the di-acrylate towards the surface region ofthe CLC layer. The result after complete photo-polymerization can bethat the surface region of the CLC layer contains more chiral materialand thus has a shorter helical pitch compared to the bottom region ofthe CLC layer, which contains a relatively higher amount of non-chiralcompound. Under some other circumstances, thermal treatment before/afteror during UV irradiation can be added in the polymerization process tocontrol the helical pitch gradient. Thus, by controlling the ratiobetween two different liquid crystal monomers and/or the dose of UVirradiation at different depths with or without thermal treatment, ahelical pitch gradient can be achieved along the depth direction of theCLC layer.

For some applications, it may be desirable to have certain opticalcharacteristics of a diffraction grating, such as off-angle diffractionefficiency, refractive index, wavelength selectivity, polarizationselectivity and phase selectivity, among other parameters, to vary alonga lateral direction orthogonal to the layer normal direction. Thelateral variation be desired, for example, when the grating is stackedwith a waveguide, e.g., as illustrated above with respect to FIGS. 6 and7, such that the light propagates in the lateral direction. Under suchconfiguration, however, the intensity of light may attenuate as itpropagates within the waveguide (e.g., 1182 in FIG. 7). Suchconfigurations may also be desirable, for example, to intentionally skewthe light intensity across the grating (e.g., 1282 in FIG. 7) to adaptto spatial and/or angular variation of sensing efficiencies associatedwith the human eye to maximize the user experience. Thus, there is aneed for optical elements, e.g., diffraction gratings, having spatiallyvarying optical characteristics.

FIG. 15 illustrates a cross-sectional side view of a CLCG including aCLC layer having lateral regions with different helical pitches along alateral direction for spatially varying Bragg-reflection. The CLC layer1424 has a plurality of lateral regions having different liquid crystalmaterial parameters, e.g., helical pitches, such that laterally varyingproperties, e.g., laterally varying off-axis incident angles for Braggreflection, can be obtained. In the illustrated embodiment, the CLClayer 1424 includes a plurality of lateral regions 1424A, 1424B and1424C each having a period Λ and having respective helical pitches p₁,p₂ and p₃. The helical pitches p₁, p₂ and p₃ can be selected such thatthe plurality of vertical regions 1424A, 1424B and 1404C are configuredfor optimum diffraction efficiency at different off-axis incident anglesθ_(incA), θ_(incB) and θ_(incC) respectively, which results in reflectedlight beams at corresponding reflection angles θ_(A), θ_(B), and θ_(C),respectively. Furthermore, as described above with respect to FIG. 13C,different lateral regions of the CLC layer 1424 are further configuredto have similar respective ranges of off-axis angles in which relativelyhigh diffraction efficiency can be obtained. Of course, while threevertical regions are illustrated for clarity, any suitable number ofregions can be included in the CLC layer 1424.

In the illustrated embodiment of FIG. 15, the magnitudes of helicalpitches p₁, p₂ and p₃ can change monotonically in a lateral direction,such that a gradient in helical pitch is created. When the rate ofchange of the helical pitch in the x-direction is uniform across a widthor a length of the CLC layer 1424, a linear relationship between thelength or width and the helical pitch can be obtained, as illustrated ingraph 1428 representing a. However, embodiments are not so limited. Forexample, the helical pitches p₁, p₂ and p₃ can increase or decrease atany lateral position and can change at different rates in thex-direction along the length or width, according to various otherembodiments.

According to various embodiments, CLC layers can be fabricated to havelaterally varying diffraction characteristics by, e.g., spatiallyvarying alignment characteristics or other material properties of theliquid crystal molecules. For example, in a similar manner as describedsupra with respect to FIG. 14, e.g., by controlling the ratio betweentwo different liquid crystal monomers and/or the dose of UV irradiationin different lateral regions, a lateral helical pitch gradient can beachieved along a lateral dimension.

Waveguides Coupled with CLCG for Wavelength-Selective Light Coupling

As described supra, for various applications including incoupling andoutcoupling of light, a wave guide device can be configured to propagatelight by total internal reflection (TIR). FIG. 16 illustrates an exampleof an optical wave-guiding device 1600 comprising a waveguide 1604coupled to a CLCG 1150. The CLCG 1150 comprises liquid crystal moleculesarranged as a plurality of chiral structures in a similar manner tochiral structures 1162-1, 1162-2, . . . 1162-i described supra withrespect to FIG. 11. The waveguide 1604 is disposed over the CLCG 1150and optically coupled to the CLCG 1150. When elliptically/circularlypolarized incident light 1016-R/L has a polarization handedness whichmatches the direction of rotation of the liquid crystal molecules of thechiral structures, the incident light 1016-R/L is Bragg-reflected by theCLCG 1150 and coupled into the waveguide 1604 at an angle such that thecoupled light travels in a lateral direction (e.g., x-direction), bytotal internal reflection (TIR). Without being bound to any theory, theTIR condition can be satisfied when the diffraction angle θ is greaterthan the critical angle, θ_(C), of the waveguide. Under somecircumstances, the TIR condition can be expressed as:sin(θ_(C))=1/n _(t)  [4]where n_(t) is the refractive index of the waveguide 1604. According tovarious embodiments, n_(t) may be between about 1 and about 2 betweenabout 1.4 and about 1.8 or between about 1.5 and about 1.7. For example,the waveguide may comprise a polymer such as polycarbonate or a glass.

FIG. 17A illustrates a first optical wave-guiding device 1700Acomprising a first waveguide 1704A coupled to a first CLCG 1750A andconfigured to propagate light having a third wavelength λ₃ by totalinternal reflection (TIR) when θ>θ_(c3). The first CLCG 1750A has afirst period Λ₁ and a first helical pitch p₁. According to someembodiments, the first wave-guiding device 1700A may be configured forpropagating light by TIR in the visible spectrum (e.g., with wavelengthsbetween about 400 nm and 700 nm). According to some other embodiments,the first wave-guiding device 1700A may be configured for propagatinglight by TIR in the infrared spectrum (e.g., in the near-infraredportion of the spectrum with wavelengths between about 700 nm and 1400nm). As described above with respect to FIGS. 10 and 11,Bragg-reflection occurs at a wavelength expressed by Eq. [1] supra andwithin a bandwidth of wavelength Δλ expressed by Eq. [2] supra. Forexample, the first CLCG 1750A may be designed for coupling by TIR thirdincident light 1736 having a third wavelength λ₃ in one of blue color(e.g., about 450 nm), green color (e.g., about 550 nm), red color (e.g.,about 650 nm) or in the infrared. As illustrated, when Δλ is about 60nm, about 80 nm or about 100 nm, as described supra, first and secondlight 1716 and 1726 having first and second wavelengths λ₁, λ₂ aresubstantially transmitted because Eq. [1] is not satisfied for thesecolors, which are not coupled into the first waveguide 1704 because Eq.[4] is not satisfied.

FIG. 17B illustrates a second optical wave-guiding device 1700B combinedwith the first optical wave-guiding device 1700A illustrated above withrespect to FIG. 17A. The optical wave-guiding device 1700B is disposedin the optical path subsequent to the optical wave-guiding device 1700A,and comprises a second waveguide 1704B coupled to a second CLCG 1750Band configured to propagate second light 1726 having a second wavelengthλ₂ by total internal reflection (TIR) when θ>θ_(c2). The second CLCG1750B has a second period Λ₂ and a second helical pitch p₂. As describedabove with respect to FIG. 17A, first and second light 1716 and 1726having first and second wavelengths of λ₁, λ₂ are substantiallytransmitted through the first optical wave-guiding device 1700A. Of thetransmitted first and second light 1716 and 1726, the second CLCG 1750Bmay be designed for coupling by TIR the second incident light 1726having the second wavelength λ₂ in transmitted one of blue color (e.g.,about 450 nm), green color (e.g., about 550 nm), red color (e.g., about650 nm) or infrared, when θ>θ_(c2). Thus, as illustrated, when Δλ isabout 60 nm, about 80 nm or about 100 nm, as described supra, firstlight 1716 having the first wavelength λ₁ is substantially transmittedfurther through the second wave-guiding device 1700B.

FIG. 17C illustrates a third optical wave-guiding device 1700C combinedthe first and second optical wave-guiding devices 1700A and 1700Billustrated above with respect to FIG. 17B. The third opticalwave-guiding device 1700C is disposed in the optical path subsequent tothe first and second optical wave-guiding devices 1700A and 1700B, andcomprises a third waveguide 1704C coupled to a third CLCG 1750C andconfigured to propagate first light 1716 having a first wavelength λ₂ bytotal internal reflection (TIR) when θ>θ_(c1). The third CLCG 1750C hasa third period Λ₃ and a third helical pitch p₃. As described above withrespect to FIG. 17B, first light 1716 having first wavelength λ₁ issubstantially is transmitted through the first and second wave-guidingdevices 1700A and 1700B. The third CLCG 1750C may be designed forcoupling by TIR the first incident light 1716 having the firstwavelength λ₁ in transmitted one of blue color (e.g., about 450 nm),green color (e.g., about 550 nm), red color (e.g., about 650 nm) orinfrared when θ>θ_(c1). Thus, as illustrated, when Δλ is about 60 nm,about 80 nm or about 100 nm, as described supra, first light 1716 havingthe first wavelength λ₁ is substantially coupled into the thirdwaveguide 1704C because Eq. [4] is satisfied.

Thus, as described above with respect to FIGS. 17A-17C, by placing oneor more of the first, second and third optical wave-guiding devices1700A, 1700B and 1700C in the same optical path, one or more of first,second and third light 1716, 1726 and 1736 having different wavelengthsλ₁, λ₂ and λ₃ can be coupled to propagate by TIR in one of first, secondand third waveguides 1704A, 1704B and 1704C, respectively. While in eachof FIGS. 17A-17C, each of the first to third optical wave-guidingdevices 1704A, 1704B and 1704C has a dedicated first to third waveguides1704A, 1704B and 1704C, respectively, and a dedicated first to thirdCLCGs 1750A, 1750B and 1750C, embodiments are not so limited. Forexample, a single waveguide can couple by TIR Bragg-reflected light froma stack of a plurality of CLCGs, as illustrated infra with respect toFIG. 18. In addition, any suitable number of optical wave-guidingdevices greater than three (or less than three) can also be combined forfurther selective coupling by Bragg-reflection.

FIG. 18 illustrates an optical wave-guiding device 1800 comprising acommon waveguide 1704 coupled to a plurality of CLCGs 1750. Theplurality of CLCGs 1750 is configured as a stack comprising the first tothird CLCGs 1750A-1750C and configured to propagate third, second andfirst light 1736, 1726 and 1716 having third, second and firstwavelengths λ₃, λ₂ and λ₁, respectively, by total internal reflection(TIR). The TIR occurs when one or more of third, second and first lights1736, 1726 and 1716, respectively, satisfies the condition θ>θ_(c3)θ>θ_(c2) and θ>θ_(c1), respectively, in a similar manner as describedabove with respect to FIGS. 17A-17C. Also in a similar manner, first,second and third CLCGs 1750A, 1750B and 1750C are configured toselectively Bragg-reflect third, second and first light 1736, 1726 and1716, respectively, when θ>θ_(c3) θ>θ_(c2) and θ>θ_(c1). Of course, anysuitable number CLCGs less than or greater than three (or less thanthree) can be stacked for further selective coupling byBragg-reflection. Thus, compared to the embodiments described above withrespect to FIGS. 17B and 17C, a more compact wave-guiding device 1800can be obtained by employing a common waveguide 1704. Also, instead ofthree distinct CLCG layers (as shown in FIG. 18), the stack of CLCGlayers could be arranged as a single (or multiple) layers having ahelical pitch gradient comprising the range from p₁ to p₃.

As described above with respect to FIGS. 17A-18, first to third CLCGs1750, 1750B, 1750C have first to third periods Λ₁, Λ₂ and Λ₃,respectively and first to third helical pitches p₁, p₂ and p₃,respectively. In various embodiments, each of the CLCGs can beconfigured such that the wavelength/period ratio λ/Λ is between about0.3 and 2.3, between about 0.8 and 1.8 or between about 1.1 and about1.5, for instance about 1.3. Alternatively, the period (Λ) can beconfigured to be between about 1 nm and 250 nm smaller, between about 50nm and 200 nm smaller or between about 80 nm and 170 nm smaller, thanthe respective wavelength (λ) that the CLCGs are configured for Braggreflection. For example, when λ₁, λ₂ and λ₃ are within the visiblerange, e.g., about 620 nm to about 780 nm, for instance about 650 nm(red), about 492 nm to about 577 nm, for instance 550 nm (green), andabout 435 nm to about 493 nm, for instance about 450 nm (blue),respectively, the corresponding periods Λ₁, Λ₂ and Λ₃ can be about 450nm to about 550 nm, for instance about 500 nm, about 373 nm to about 473nm, for instance about 423 nm, and about 296 nm to about 396 nm, forinstance about 346 nm, respectively. Alternatively, when λ₁, λ₂ and λ₃are in the infrared range, e.g., in the near infrared range betweenabout 750 nm to about 1400 nm, for instance about 850 nm, thecorresponding periods Λ₁, Λ₂ and Λ₃ can be about 975 nm to about 1820nm, for instance about 1105 nm. In addition, various embodiments, eachof the CLCGs can be configured such that the wavelength/helical pitchratio λ/p is between about 0.6 and 2.6, between about 1.1 and 2.1 orbetween about 1.4 and about 1.8, for instance about 1.6. Alternatively,the helical pitch (p) can be configured to be between about 50 nm and350 nm smaller, between about 100 nm and 300 nm smaller or between about140 nm and 280 nm smaller, than the respective wavelength (λ) that theCLCGs are configured for Bragg reflection. For example, when λ₁, λ₂ andλ₃ are about 620 nm to about 780 nm, for instance about 650 nm (red),about 492 nm to about 577 nm, for instance 550 nm (green), and about 435nm to about 493 nm, for instance about 450 nm (blue), respectively, thecorresponding helical pitches p₁, p₂ and p₃ can be about 350 nm to about450 nm, for instance about 400 nm, about 290 nm to about 390 nm, forinstance about 340 nm and about 230 nm to about 330 nm, for instanceabout 280 nm, respectively. Alternatively, when λ₁, λ₂ and λ₃ are in theinfrared range, e.g., in the near infrared range between about 750 nm toabout 1400 nm, for instance about 850 nm, the corresponding periods Λ₁,Λ₂ and Λ₃ can be about 1200 nm to about 2240 nm, for instance about 1360nm.

Waveguides Coupled with CLCG and a Mirror for Wavelength-Selective LightCoupling

FIG. 19 illustrates an optical wave-guiding device 1900 comprising awaveguide 1604 coupled to a CLCG 1150, similar to the opticalwave-guiding device described supra with respect to FIG. 16. Asdescribed supra with respect to FIGS. 10 and 11, in operation, when thehandedness of polarization of the elliptical/circularly polarizedincident light has the same direction of rotation as the liquid crystalmolecules of the chiral structures of the CLCG 1150, the CLCG 1150substantially reflects the incident light. As illustrated, incident onthe surface 1050S are light beams 1016-L having a left-handed circularpolarization and light beams 1016-R having a right-handed circularpolarization. In the illustrated embodiment, the liquid crystalmolecules of the chiral structures are successively rotated in aclockwise direction when viewing the direction in which incident lightbeams 1016-L, 1016-R travel, i.e., the negative z-direction, such thatthe rotation direction of the liquid crystal molecules match thehandedness of the light teams 1016-R having a right-handed circularpolarization. As a result, the light beams 1016-R having a right-handedcircular polarization are substantially reflected by the CLCG 1150,whereas the light beams 1016-L having a left-handed circularpolarization are substantially transmitted through the CLCG 1150.

For some applications, it may desirable to flip the polarizationhandedness of an elliptical or circular polarized light prior tocoupling into a wave-guiding device similar to that described above withrespect to FIG. 19. Such may the case, e.g., when the polarizationhandedness of the incident elliptical or circular polarized light doesnot match the rotation direction of the chiral structures in the CLCGsuch that the CLCG is not configured to be Bragg-reflect the light forcoupling into the waveguide, as discussed supra. For some otherapplications, it may be desirable to recycle light that is transmittedthrough the CLCG due to a lack of match between the polarizationhandedness of the incident elliptical or circular polarized light andthe rotation direction of the chiral structures in the CLCG. To addressthese and other needs, in the following, various embodiments ofwave-guiding devices employing a polarization converting reflector toaddress these needs are disclosed.

FIG. 20 illustrates an optical wave-guiding device 2000 comprising awaveguide 1150 coupled to a CLCG 1604 and a polarization convertingreflector 2004, where the CLCG 1604 is configured to receive incidentlight and the waveguide 1150 is configured to propagate lightBragg-reflected from the CLCG by total internal reflection (TIR). Thepolarization converting reflector 2004 is configured such that, uponreflection therefrom, the polarization handedness of an incidentelliptically or circularly polarized light is flipped to an oppositepolarization handedness (e.g., left-handed to right-handed, orright-handed to left-handed). The wave-guiding device 2000 is similar tothe wave-guiding device 1900 described above with respect to FIG. 19except, instead of being configured to first receive an incident lightbeam through the waveguide 1150, the wave-guiding device 2000 isconfigured to first receive an incident light beam 2016-L having, e.g.,a left-handed circular polarization, through the CLCG 1604. The incidentlight beam 2016-L has a polarization handedness that does not match therotation direction of the chiral structures in the CLCG 1604 when viewedin the propagation direction (negative z-direction) of the incidentlight beam 2016-L, such that it is not Bragg-reflected by the CLCG 1604.As a result, the incident light beam 2016-L is substantially transmittedthrough the CLCG 1604 and subsequently reflected by the polarizationconverting reflector 2004. The reflected light beam 2016-R having, e.g.,a right-handed circular polarization, thereby becomes an incident lightbeam on the surface 1150S of the waveguide 1150. Because of the flippedpolarization handedness, the reflected light beam 2016-R now incident onsurface 1150S of the waveguide 1150 has a polarization handedness thatmatches the rotation direction of the chiral structures in the CLCG 1604when viewed in the propagation direction of reflected light beam 2016-R(positive z-direction), such that it is Bragg-reflected by the CLCG1604. The reflected light beam 2016-R that is reflected as furtherreflected beam 2018 reflected at an angle θ>θ_(c) relative to the layernormal direction (z-axis) couples to and travels through the waveguide1150 in a lateral direction (e.g., x-direction).

FIG. 21A illustrates the optical wave-guiding device 2000 describedabove with respect to FIG. 20 under a condition in which the incidentlight beam 2116 is linearly polarized or unpolarized, each of which canbe treated as comprising both left-handed and right-handed circularpolarization components. Under such conditions, the incident light beam2116 can be coupled into a waveguide by TIR in opposing lateraldirections. For example, similar to as described above with respect toFIG. 20, the component of the incident light beam 2116 that has apolarization handedness, e.g., left-handedness, that does not match therotation direction of the chiral structures in the CLCG 1604 issubstantially transmitted through the CLCG 1604 and subsequentlyreflected by the polarization converting reflector 2004, to be flippedin polarization handedness, e.g., flipped to right-handedness, andcoupled into and travels through the waveguide 1150 in a first lateraldirection (e.g., positive x-direction). On the other hand, similar to asdescribed above with respect to FIG. 19, the component of the incidentlight beam 2116 that has a polarization handedness, e.g.,right-handedness, that matches the rotation direction of the chiralstructures in the CLCG 1604, is substantially directly reflected by theCLCG 1604 and subsequently coupled into and travels through thewaveguide 1150 in a second lateral direction opposite the first lateraldirection (e.g., negative x-direction).

FIG. 21B illustrates the optical wave-guiding device 2000 describedabove with respect to FIG. 21A under a condition in which the incidentlight is polarized into two orthogonal elliptical or circular polarizedlight beams, e.g., light beams 1016-L having left-handed circularpolarization and light beams 1016-R having right-handed circularpolarization. Under such conditions, the incident light beams 1016-L,1016-R can be coupled into a waveguide by TIR to propagate in opposinglateral directions, in a similar manner as described with respect toFIG. 21A, supra. For example, the light beams 1016-L that has apolarization handedness, e.g., left-handedness, that does not match therotation direction of the chiral structures in the CLCG 1604 issubstantially transmitted through the CLCG 1604 and subsequentlyreflected by the polarization converting reflector 2004, to be flippedin polarization handedness, e.g., flipped to right-handedness, andcoupled into and travels through the waveguide 1150 in a first lateraldirection (e.g., positive x-direction). On the other hand, the incidentlight beam 1016-R that has a polarization handedness, e.g.,right-handedness, that matches the rotation direction of the chiralstructures in the CLCG 1604, is substantially directly reflected by theCLCG 1604 and subsequently coupled into and travels through thewaveguide 1150 in a second lateral direction opposite the first lateraldirection (e.g., negative x-direction).

FIG. 22A illustrates an optical wave-guiding device 2200 comprising acommon waveguide 2204 coupled to a plurality of CLCGs that are, e.g.,arranged as a stack, including a first CLCG 2204 having chiralstructures having a first rotation direction and a second CLCG 2208having chiral structures having a second rotation direction opposite tothe first rotation direction. As described supra with respect to variousembodiments, in operation, when the direction of polarization directionof an incident light beam is matched to the direction of rotation of theliquid crystal molecules of chiral structures of a CLCG, the incidentlight is reflected. The illustrated optical wave-guiding device 2200 isunder a condition in which the incident light beam 2116 is linearlypolarized or unpolarized. Under such conditions, the incident light beam2116 can be coupled into a waveguide by TIR in both of opposing lateraldirections (positive and negative x directions). In the illustratedembodiment, when viewing in the direction in which incident light 2116travels, i.e., the negative z-direction, the liquid crystal molecules ofthe chiral structures of the first CLCG 2204 are successively rotated ina clockwise direction, while the liquid crystal molecules of the chiralstructures of the second CLCG 2204 are successively rotated in theopposite counterclockwise direction.

Still referring to FIG. 22A, the component of the elliptical or circularincident light beam 2116 that has a first polarization handedness, e.g.,right-handed polarized component, that matches the rotation direction ofthe chiral structures of the first CLCG 2204, e.g., clockwise direction,is substantially reflected by the first CLCG 2204, thereby resulting ina first reflected beam 2118A at an angle θ>θ_(c1) relative to the layernormal direction (z-axis), and couples to and travels through the commonwaveguide 2204 in a first lateral direction (e.g., positivex-direction).

Still referring to FIG. 22A, on the other hand, the component of theelliptical or circular incident light beam 2116 that has a secondpolarization handedness, e.g., left-handed polarized component, thatdoes not match the rotation direction of the chiral structures of thefirst CLCG 2204, is substantially transmitted through the first CLCG2204. After being transmitted through the first CLCG 2204, theelliptical or circular incident light beam 2116 that has the secondpolarization handedness 2116 that does match the rotation direction ofthe chiral structures of the second CLCG 2208, e.g., counter-clockwisedirection, is substantially reflected by the second CLCG 2208, therebyresulting in a second reflected beam 2118B at an angle θ>θ_(c2) relativeto the layer normal direction (z-axis), and couples to and travelsthrough the common waveguide 2204 in a second lateral direction (e.g.,negative x-direction).

FIG. 22B illustrates the optical wave-guiding device 2000 describedabove with respect to FIG. 22A under a different condition in which theincident light is polarized into two orthogonal elliptical or circularpolarized light beams, e.g., light beams 1016-L having, e.g., aleft-handed elliptical/circular polarization and light beams 1016-Rhaving, e.g., a right-handed elliptical/circular polarization. Undersuch condition, the incident light beams 1016-L, 1016-R can be coupledinto the common waveguide 2204 by TIR in opposing lateral directions, ina similar manner as described with respect to FIG. 22A, supra, forcoupling the incident light beams 1016-L, 1016-R having first and secondpolarization handedness, e.g., left-handedness and right-handedness.

The embodiments described above with respect to FIGS. 21B and 22B can beparticularly advantageous in certain applications, e.g., where differentlight signals (e.g., images) are encoded in orthogonal circularpolarizations. Under such circumstances, light can be coupled into theopposite directions (e.g., positive and negative x-directions) dependingon the polarization handedness.

FIG. 22C illustrates an optical wave-guiding device 2220 comprising acommon waveguide 2250 coupled to a plurality of CLCGs, e.g., arranged asa stack, including a first CLCG 2204 having chiral structures having afirst rotation direction and a second CLCG 2208 having chiral structureshaving a second rotation direction opposite to the first rotationdirection. Unlike the embodiments described with respect to FIGS. 22Aand 22B, in the wave-guiding device 2220, the common waveguide 2250 isinterposed between the first and second CLCG layers 2204, 2208. Forillustrative purposes, the illustrated optical wave-guiding device 2220is under a condition in which the incident light beam 2116 is linearlypolarized or unpolarized. Under such conditions, the incident light beam2116 can be coupled into a waveguide by TIR in opposing lateraldirections. In the illustrated embodiment, when viewing the direction inwhich incident light 2116 travels, i.e., the negative z-direction, theliquid crystal molecules of the chiral structures of the first CLCG 2204are successively rotated in a clockwise direction, while the liquidcrystal molecules of the chiral structures of the second CLCG 2204 aresuccessively rotated in the opposite counterclockwise direction. Ofcourse, opposite arrangement is possible.

Still referring to FIG. 22C, the component of the elliptical or circularincident light beam 2116 that has a first polarization handedness, e.g.,right-handed polarized component, that matches the rotation direction ofthe chiral structures of the first CLCG 2204, e.g., clockwise direction,is substantially reflected by the first CLCG 2204, thereby resulting ina first reflected beam 2118A at an angle θ>θ_(c1) relative to the layernormal direction (z-axis), which in turn reflects off of the outersurface of the first CLCG 2204, before coupling into and travelingthrough the common waveguide 2250 in a first lateral direction (e.g.,negative x-direction) by TIR.

Still referring to FIG. 22C, on the other hand, the component of theelliptical or circular incident light beam 2116 that has a secondpolarization handedness, e.g., left-handed polarized component, thatdoes not match the rotation direction of the chiral structures of thefirst CLCG 2204, e.g., clockwise direction, is substantially transmittedthrough the first CLCG 2204 and further through the common waveguide2204, and thereafter substantially reflected by the second CLCG 2208,thereby resulting in a second reflected beam 2218B at an angle θ>θ_(c2)relative to the layer normal direction (z-axis), and couples to andtravels through the common waveguide 2250 in a second lateral direction(e.g., positive x-direction) by TIR.

Cholesteric Liquid Crystal Off-Axis Mirror

As described supra with respect to various embodiments, by matching thehandedness of polarization of incident elliptically or circularlypolarized light with the direction of rotation as the liquid crystalmolecules of the chiral structures of a CLC layer, the CLC layer can beconfigured as a Bragg reflector. Furthermore, one or more CLC layershaving different helical pitches can be configured as a wave-lengthselective Bragg reflector with high bandwidth. Based on the conceptsdescribed herein with respect to various embodiments, the CLC layers canbe configured as an off-axis mirror configured to selectively reflect afirst range of wavelengths, for example, infrared wavelengths (e.g., thenear infrared), while transmitting another range of wavelengths, e.g.,visible wavelengths. In the following, applications of variousembodiments of CLC off-axis mirrors implemented in eye-tracking systemsare disclosed.

FIG. 23 illustrates an example of an eye-tracking system 2300 employinga cholesteric liquid crystal reflector (CLCR), e.g., awavelength-selective CLCR 1150 configured to image an eye 302 of aviewer, according to various embodiments. Eye tracking can be a keyfeature in interactive vision or control systems including wearabledisplays, e.g., the wearable display system 200 in FIG. 2 or the systems700 described in FIGS. 24A-24H, for virtual/augmented/mixed realitydisplay applications, among other applications. To achieve good eyetracking, it may desirable to obtain images of the eye 302 at lowperspective angles, for which it may in turn be desirable to dispose aneye-tracking camera 702 b near a central position of viewer's eyes.However, such position of the camera 702 b may interfere with user'sview. Alternatively, the eye-tracking camera 702 b may be disposed to alower position or a side. However, such position of the camera mayincrease the difficulty of obtaining robust and accurate eye trackingsince the eye images are captured at a steeper angle. By configuring theCLCR 1150 to selectively reflect infrared (IR) light 2308 (e.g., havinga wavelength of 850 nm) from the eye 302 while transmitting visiblelight 2304 from the world as shown in FIG. 4, the camera 702 b can beplaced away from the user's view while capturing eye images at normal orlow perspective angles. Such configuration does not interfere withuser's view since visible light is not reflected. The same CLCR 1150 canalso be configured as an IR illumination source 2320, as illustrated. Alow perspective angle of IR illuminator can results in less occlusions,e.g., from eye lashes, which configuration allows more robust detectionof specular reflections, which can be key feature in modern eye-trackingsystems.

Still referring to FIG. 23, according to various embodiments, the CLCR1150 comprises one or more cholesteric liquid crystal (CLC) layers eachcomprising a plurality of chiral structures, wherein each chiralstructure comprises a plurality of liquid crystal molecules that extendin a layer depth direction (e.g., z-direction) and are successivelyrotated in a first rotation direction, as described supra. Thearrangements of the liquid crystal molecules of the chiral structuresvary periodically in a lateral direction perpendicular to the layerdepth direction such that the one or more CLC layers are configured tosubstantially Bragg-reflect a first incident light having a firstwavelength (λ₁) while substantially transmitting a second incident lighthaving a second wavelength (λ₂). As described elsewhere in thespecification, each of the one or more CLC layers are configured tosubstantially Bragg-reflect elliptically or circularly polarized firstand second incident light having a handedness of polarization that ismatched to the first rotation direction, when viewed in the layer depthdirection, while being configured to substantially transmit ellipticallyor circularly polarized first and second incident light having ahandedness of polarization that is opposite to the first rotationdirection, when viewed in the layer depth direction. Accordingembodiments, the arrangements of the liquid crystal molecules varyingperiodically in the lateral direction are arranged to have a period inthe lateral direction such that a ratio between the first wavelength andthe period is between about 0.5 and about 2.0. According to embodiments,the first wavelength is in the near infrared range between about 600 nmand about 1.4 m, for instance about 850 nm and the second wavelength inis in the visible range having one or more colors as described elsewherein the specification. According to embodiments, the liquid crystalmolecules of the chiral structures are pre-tilted relative to adirection normal to the layer depth direction. As configured, the one ormore CLC layers are configured such that the first incident light isreflected at an angle (θ_(R)) relative to the layer depth direction(z-direction) exceeding about 50°, about 60°, about 70 or about 800degrees relative to the layer depth direction based on, e.g., Eq. [3]described supra.

Referring back to FIG. 2, the eyes of the wearer of a head mounteddisplay (HMD) (e.g., the wearable display system 200 in FIG. 2) can beimaged using a reflective off-axis Diffractive Optical Element (DOE),which may be for example, a Holographic Optical Element (HOE). Theresulting images can be used to track an eye or eyes, image the retina,reconstruct the eye shape in three dimensions, extract biometricinformation from the eye (e.g., iris identification), etc.

There are a variety of reasons why a head mounted display (HMD) mightuse information about the state of the eyes of the wearer. For example,this information can be used for estimating the gaze direction of thewearer or for biometric identification. This problem is challenging,however, because of the short distance between the HMD and the wearer'seyes. It is further complicated by the fact that gaze tracking requiresa larger field of view, while biometric identification requires arelatively high number of pixels on target on the iris. For an imagingsystem which will attempt to accomplish both of these objectives, therequirements of the two tasks are largely at odds. Finally, bothproblems are further complicated by occlusion by the eyelids andeyelashes. Embodiments of the imaging systems described herein addresssome or all of these problems. The various embodiments of the imagingsystems 700 described herein with reference to FIGS. 24A-24F can be usedwith HMD including the display devices described herein (e.g., thewearable display system 200 shown in FIG. 2 and/or the display system1000 shown in FIG. 6).

FIG. 24A schematically illustrates an example of an imaging system 700that comprises an imager 702 b which is used to view the eye 304, andwhich is mounted in proximity to the wearer's temple (e.g., on a frame64 of the wearable display system 200, FIG. 2, for example, an earstem). In other embodiments, a second imager is used for the wearer'sother eye 302 so that each eye is separately imaged. The imager 702 bcan include an infrared digital camera that is sensitive to infraredradiation. The imager 702 b is mounted so that it is facing forward (inthe direction of the wearer's vision), rather than facing backward anddirected at the eye 304 (as with the camera 500 shown in FIG. 6). Bydisposing the imager 702 b nearer the ear of the wearer, the weight ofthe imager 702 b is also nearer the ear, and the HMD may be easier towear as compared to an HMD where the imager is backward facing anddisposed nearer to the front of the HMD (e.g., close to the display 62,FIG. 2). Additionally, by placing the forward-facing imager 702 b nearthe wearer's temple, the distance from the wearer's eye 304 to theimager is roughly twice as large as compared to a backward-facing imagerdisposed near the front of the HMD (e.g., compare with the camera 500shown in FIG. 4). Since the depth of field of an image is roughlyproportional to this distance, the depth of field for the forward-facingimager 702 b is roughly twice as large as compared to a backward-facingimager. A larger depth of field for the imager 702 b can be advantageousfor imaging the eye region of wearers having large or protruding noses,brow ridges, etc.

The imager 702 b is positioned to view an inside surface 704 of anotherwise transparent optical element 706. The optical element 706 canbe a portion of the display 708 of an HMD (or a lens in a pair ofeyeglasses). The optical element 706 can be transmissive to at least10%, 20%, 30%, 40%, 50%, or more of visible light incident on theoptical element. In other embodiments, the optical element 706 need notbe transparent (e.g., in a virtual reality display). The optical element706 can comprise a CLC off-axis mirror 708. The CLC off-axis mirror 708can be a surface reflecting a first range of wavelengths while beingsubstantially transmissive to a second range of wavelengths (that isdifferent from the first range of wavelengths). The first range ofwavelengths can be in the infrared, and the second range of wavelengthscan be in the visible. For example, the CLC off-axis mirror 708 cancomprise a hot mirror, which reflects infrared light while transmittingvisible light. In such embodiments, infrared light 710 a, 712 a, 714 afrom the wearer propagates to and reflects from the optical element 706,resulting in reflected infrared light 710 b, 712 b, 714 b which can beimaged by the imager 702 b. In some embodiments, the imager 702 b can besensitive to or able to capture at least a subset (such as a non-emptysubset and/or a subset of less than all) of the first range ofwavelengths reflected by the CLC off-axis mirror 708. For example, theCLC off-axis mirror 708 may reflect infrared light in the a range of 700nm to 1.5 μm, and the imager 702 b may be sensitive to or able tocapture near infrared light at wavelengths from 700 nm to 900 nm. Asanother example, the CLC off-axis mirror 708 may reflect infrared lightin the a range of 700 nm to 1.5 μm, and the imager 702 b may include afilter that filters out infrared light in the range of 900 nm to 1.5 μmsuch that the imager 702 b can capture near infrared light atwavelengths from 700 nm to 900 nm.

Visible light from the outside world (1144, FIG. 6) is transmittedthrough the optical element 706 and can be perceived by the wearer. Ineffect, the imaging system 700 shown in FIG. 24A acts as if there were avirtual imager 702 c directed back toward the wearer's eye 304. Thevirtual imager 702 c can image virtual infrared light 710 c, 712 c, 714c (shown as dotted lines) propagated from the wearer's eye 704 throughthe optical element 706. Although the hot mirror (or other DOE describedherein) can be disposed on the inside surface 704 of the optical element706, this is not a limitation. In other embodiments, the hot mirror orDOE can be disposed on an outside surface of the optical element 706 orwithin the optical element 706 (e.g., a volume HOE).

FIG. 24B schematically illustrates another example of the imaging system700. In this embodiment, perspective distortions may be reduced oreliminated by the use of a perspective control lens assembly 716 b(e.g., a shift lens assembly, a tilt lens assembly, or a tilt-shift lensassembly) with the imager 702 b. In some embodiments, the perspectivecontrol lens assembly 716 b may be part of the lens of the imager 702 b.The perspective control lens 716 b can be configured such that a normalto the imager 702 b is substantially parallel to a normal to the regionof the surface 704 that includes the DOE (or HOE) or hot mirror. Ineffect, the imaging system 700 shown in FIG. 24B acts as if there were avirtual imager 702 c with a virtual perspective control lens assembly716 c directed back toward the wearer's eye 304.

Additionally or alternatively, as schematically shown in FIG. 24C, theCLC off-axis mirror 708 of the optical element 706 may have, on itssurface 704, an off axis holographic mirror (OAHM), which is used toreflect light 710 a, 712 a, 714 a to facilitate viewing of the eye 304by the camera imager 702 b which captures reflected light 710 b, 712 b,714 b. The OAHM 708 may have optical power as well, in which case it canbe an off-axis volumetric diffractive optical element (OAVDOE), asschematically shown in FIG. 24D. In the example shown in FIG. 24D, theeffective location of the virtual camera 702 c is at infinity (and isnot shown in FIG. 24D).

In some embodiments, the HOE (e.g., the OAHM or OAVDOE) can be dividedinto a plurality of segments. Each of these segments can have differentoptical properties or characteristics, including, for example,reflection angles at which the segments reflect the incoming (infrared)light or optical power. The segments can be configured so that light isreflected from each segment toward the imager 702 b. As a result, theimage acquired by the imager 702 b will also be divided into acorresponding number of segments, each effectively viewing the eye froma different angle. FIG. 24E schematically illustrates an example of thedisplay system 700 having an OAHM with three segments 718 a 1, 718 a 2,718 a 3, each of which acts as a respective virtual camera 702 c 1, 702c 2, 702 c 3 imaging the eye 304 at a different angular location.

FIG. 24F schematically illustrates another example of the display system700 having an OAHM with three segments 718 a 1, 718 a 2, 718 a 3, eachhaving optical power (e.g., a segmented OAVDOE), with each segmentgenerating a virtual camera at infinity imaging the eye 304 at adifferent angular location. Although three segments are schematicallyillustrated in FIGS. 24E and 24F, this is for illustration and notlimitation. In other embodiments, two, four, five, six, seven, eight,nine, or more segments can be utilized. None, some, or all of thesesegments of the HOE can have optical power.

The three segments 718 a 1, 718 a 2, 718 a 3 are shown as spacedhorizontally across the optical element 706 in FIGS. 24E and 24F. Inother embodiments, the segments can be spaced vertically on the opticalelement 706. For example, FIG. 24G schematically shows a DOE 718 havingtwo vertically spaced segments 718 a 1 and 718 a 2, with the segment 718a 1 comprising a CLC off-axis mirror configured to reflect light backtoward the imager 702 b (which may be in the same general horizontalplane as the segment 718 a 1), and the segment 718 a 2 configured toreflect light upwards toward the imager 702 b. Similar to bifocallenses, the arrangement shown in FIG. 24G can be advantageous inallowing the imaging system 700 to use reflection imagery acquired bythe imager 702 b from the upper segment 718 a 1 when the wearer islooking forward through the upper portion of the HMD (schematicallyshown via the solid arrowed line) and to use reflection imagery from thelower segment 718 a 2 when the wearer is looking downward through thelower portion of the HMD (schematically shown via the dashed arrowedline).

A mix of horizontally spaced and vertically spaced segments can be usedin other embodiments. For example, FIG. 24H shows another example of theHOE 718 with a 3×3 array of segments each comprising a CLC off-axismirror. The imager 702 b can acquire reflection data from each of thesenine segments, which represent light rays coming from different areas ofand angular directions from the eye region. Two example light rayspropagating from the eye region to the HOE 718 and reflecting back tothe imager 702 b are shown as solid and dashed lines. The imaging system700 (or processing module 224 or 228) can analyze the reflection datafrom the plurality of segments to multiscopically calculate thethree-dimensional shape of the eye or the gaze direction (e.g., eyepose) of the eye.

Embodiments of the optical system 700 utilizing segments may havemultiple benefits. For example, the segments can be used individually,by selecting the particular segments which best suit a particular task,or they can be used collectively to multiscopically estimate thethree-dimensional shape or pose of the eye. In the former case, thisselectivity can be used to, for example, select the image of thewearer's iris which has the least occlusion by eyelids or eyelashes. Inthe latter case, the three dimensional reconstruction of the eye can beused to estimate orientation (by estimation of, for example, thelocation of the bulge of the cornea) or accommodation state (byestimation of, for example, the lens induced distortion on the apparentlocation of the pupil).

Polarization Converters Based on Notch Reflectors

To realize light-field displays, focus of virtual images should beadjusted to resolve vergence-accommodation conflicts. Variable focuslenses can be placed to change the focus of virtual images between thedisplay and user's eyes. However, most of variable/switchable focuslenses are polarization sensitive while projected virtual images may notbe well polarized. Such displays may require polarization insensitivelenses (often a pair of lens sets) or a polarizer (reducing >50% inbrightness due to the loss of light in the non-transmittedpolarization). Efficient conversion of virtual image polarization isdesired to make compact/light-efficient variable focus light-fielddisplays.

For generating virtual images in augmented reality displays, a number ofnarrow-band sources (e.g., red, green, blue (RBG) LEDs or lasers) areoften used. A waveguide-based display system can be constructed withdiffractive optical elements to project images into user's eyes. Theprojected image often does not preserve polarization purity even when awell-defined polarization of the image is injected into the waveguide.

As described herein, a notch reflector generally refers to a lightreflector that transmits most wavelengths of light substantiallyunaltered, but reflects light in a specific range of wavelengths withrelatively high efficiency. The specific range of wavelengths wherelight is reflected is termed the “notch.” A notch reflector is sometimesalso referred to as a narrow band reflector. The wavelength range in thenotch may be, e.g., <10 nm, <50 nm, <100 nm, <250 nm, or a differentrange including a range defined by any two of these values. Notchreflectors can be formed from multiple dielectric layers (amulti-layer), liquid crystals, metamaterials, metastructures, etc. Notchreflectors can include diffractive optical elements, surface orvolumetric holograms, etc. Notch reflectors can be laminated onto asubstrate material (e.g., polymer or glass). In many of theimplementations described herein, to reflect RGB light, the reflectorcomprises multiple notch reflectors, with the notch in each reflectortuned to one of the specific RGB colors (e.g., a reflector comprising anR-notch reflector, a G-notch reflector, and a B-notch reflector).Accordingly, the wavelength range of each notch can match the wavelengthrange of the light injected into the display (e.g., the R-notch ismatched to the wavelength range of the red light injected by a red LEDor laser, and similarly for the G and B notches).

Various embodiments described herein comprise a notch reflector thatincludes a transmissive substrate, e.g., a polished glass or polymersubstrate, having formed thereon one or more active layers. As describedherein, an active layer comprises a layer or a coating configured toprovide one or more of notch reflecting characteristics describe herein.The one or more active layers are configured to notch-reflect lighthaving a wavelength range Δλ of about 50 nm, about 70 nm, about 100 nmabout 150 nm, or in a range less than any of these values or in a rangedefined by any two of these values, where the range is centered around ared light including light of one or more wavelengths in the range ofabout 620-780 nm, a green light including light of one or morewavelengths in the range of about 492-577 nm, or blue light includinglight of one or more wavelengths in the range of about 435-493 nm. Insome embodiments, the wavelength range Δλ may substantially cover thered light range of about 620-780 nm, the green light range of about492-577 nm, or blue light range of about 435-493 nm.

Various embodiments described herein comprise a notch reflectorconfigured as a polarizing notch reflector. Within the notch-reflectiverange, a polarizing notch reflector allows light having one polarity tosubstantially pass therethrough, while substantially reflecting lighthaving the opposite polarity. For example, when light having bothleft-hand circular polarization (LHCP) and right-hand circularpolarization (RHCP) within the notch-reflective range is incident on apolarizing notch reflector, the notch reflector can substantiallyreflect light having one of the RHCP and LHCP, while substantiallypassing light having the opposite one of the RHCP and LHCP. Similarly,when light having both linear vertical polarization (LVP) and linearhorizontal polarization (LHP) is incident on a polarizing notchreflector, the notch reflector can substantially reflect light havingone of the LVP and LHP, while substantially passing light having theopposite one of the LVP and LHP.

Various embodiments described herein comprise a notch reflectorconfigured as a non-polarizing notch reflector. Within thenotch-reflective range, a non-polarizing notch reflector substantiallyreflects light incident thereon regardless of its polarization. Forexample, when light having both LHCP and RHCP within thenotch-reflective range is incident on a non-polarizing notch reflector,the notch reflector can substantially reflect light having both the RHCPand LHCP, Similarly, when light having both LVP and LHP is incident on apolarizing notch filter, the notch filter can substantially reflectlight having both the LVP and LHP.

In various embodiments described herein, a notch reflector configured asa polarizing or non-polarizing notch reflector can also be configuredindependently as a polarization-converting notch reflector. Within thenotch-reflective range, upon reflecting light having a polarization, thepolarization-converting notch reflector converts the polarization of thereflected light to an opposite polarity. For example, when light havingone of LHCP and RHCP within the notch-reflective range is incident on apolarization-converting notch reflector, the notch reflector convertsthe one of the RHCP and LHCP into an opposite one of the RHCP and LHCP.Similarly, when light having one of LVP and LHP is incident on apolarization converting notch reflector, the notch reflector convertsthe one of the LVP and LHP into an opposite one of the LVP and LHP.

As described herein, within the notch-reflective range (Δλ), a notchreflector configured to reflect light having one or more polarizationscan be configured to reflect substantially all of the light having theone or more polarizations the incident thereon. For example, when anotch reflector is configured to reflect light having one or both of theRHCP and LHCP, the notch reflector may reflect, e.g., greater than 80%,greater than 90%, greater than 95%, greater than 99%, greater than99.99%, greater than 99.999%, or greater than 99.9999% of the lighthaving the one or both of the RHCP and LHCP incident thereon. On theother hand, when a notch reflector is configured to reflect light havingone but not the other of the RHCP and LHCP, the notch reflector mayreflect, e.g., greater than 80%, greater than 90%, greater than 95%,greater than 99%, greater than 99.99%, greater than 99.999%, or greaterthan 99.9999% of the light having the one but not the other of the RHCPand LHCP incident thereon. Conversely, the notch reflector is configuredsuch that light that is not reflected, e.g., light having a wavelengthoutside the notch-reflective range (Δλ) or a polarization that the notchreflector is not configured to reflect, is substantially entirelytransmitted, e.g., greater than 80%, greater than 90%, greater than 95%,greater than 99%, greater than 99.99%, greater than 99.999%, or greaterthan 99.9999% of the light incident thereon may be transmitted.

In some display devices described herein, it may be desirable to recyclesome light that is outcoupled from a waveguide. For example, while thewaveguide may outcouple light having more than one polarization, anoptical element such as a lens, e.g., a transmissive or reflective lens,that is configured to exert an optical function, e.g., optical power, tothe outcoupled light prior to being viewed by the user, may bepolarization-selective. Under some circumstances, light having apolarization that the optical element is not configured to exert theoptical function may be transmitted without being viewed by the user.For example, a lens coupled to the waveguide might be configured toexert optical power to light having a polarization, e.g., one of RHCP orLHCP, while transmitting therethrough light having another polarization,e.g., the other of RHCP or LHCP, due to a lack of match between thepolarization handedness of the incident elliptical or circular polarizedlight and the rotation direction of the chiral structures in the CLCG.In these circumstances, it may be desirable to recycle light having theother of RHCP or LHCP to deliver a viewing experience to the user withhigher brightness. To address these and other needs, in the following,various embodiments of wave-guiding devices employing one or morepolarization converting reflector to address these needs are disclosed.

Example Circular Polarization Converting Display Devices

FIG. 25A illustrates a display device 2500A configured to output imageinformation to a user. The display device 2500A comprises a waveguideassembly 2504, also referred to as an eye-piece, interposed between anon-polarizing notch reflector 2508 and a polarizing notch reflector2512. In various embodiments, the waveguide assembly 2504 can beconfigured in a similar manner as the waveguide assembly 1178 describedabove with respect to FIG. 6. Similar to the configuration describedabove with respect to FIG. 6, in operation, the display device 2500Awould be disposed between the world 1114 and the eye 4, such that theeye 4 receives light from both the display device 2500A as well as fromthe world 1114.

In particular, in various embodiments described herein, the waveguideassembly 2504 of the display device 2500A comprises one or morewaveguides (e.g., 1182, 1184, 1186, 1188, 1190 in FIG. 6) eachconfigured to propagate light within each respective waveguide by totalinternal reflection (TIR) in the x-direction. The light propagatinggenerally in the x-direction, may be output, e.g., using out-couplingoptical elements or light extracting optical elements (e.g., 1282, 1284,1286, 1288, 1290 in FIG. 6) that are configured to extract light out ofa waveguide by redirecting the light, propagating within each respectivewaveguide, out of the waveguide, to output image information to the eye4 in the z-direction. In various embodiments, while not shown forclarity, the waveguide assembly 2504 may include any of CLCGs formed ofone or more CLC layers configured as out-coupling optical elements, asdescribed above. Various other details of the waveguide assembly 2504described above are omitted herein.

Still referring to FIG. 25A, the non-polarizing notch reflector 2508according to various embodiments described herein is configured suchthat, within the notch-reflective range, the non-polarizing notchreflector 2508 substantially reflects light incident thereon regardlessof its polarization. Furthermore, in the illustrated embodiment, thenon-polarizing reflector is configured as a polarization-convertingnotch reflector such that, within the notch-reflective range, uponreflecting light having a polarization, the polarization-convertingnotch reflector converts the polarization of the reflected light to anopposite polarity. The non-polarizing notch reflector 2508 includes atransmissive substrate, e.g., a polished glass or polymer substrate,having formed thereon one or more active layers. In some embodiments ofthe notch reflectors described herein, the one or more active layersformed on a substrate can include one or more dielectric coatings, whosecombination gives rise to the various notch-reflective characteristicsdescribed above.

Still referring to FIG. 25A, the polarizing notch reflector 2512according to various embodiments described herein is configured suchthat, within the notch-reflective range, the polarizing notch reflector2512 substantially reflects light incident thereon in apolarization-selective manner. Furthermore, in the illustratedembodiment, the polarizing reflector 2512 is configured such that,unlike the non-polarizing notch reflector 2508, the polarizing notchreflector 2512 is not configured as a polarization converting notchreflector such that, upon reflecting light having a polarization thepolarizing notch reflector 2512 does not convert the polarization of thereflected light to an opposite polarity. The polarizing notch reflector2512 includes a transmissive substrate, e.g., a polished glass orpolymer substrate, having formed thereon one or more active layers. Insome embodiments of the notch reflectors described herein, the one ormore active layers formed on a substrate can include one or morecholesteric liquid crystal (CLC) layers. The one or more active layersformed on a substrate can include one or more cholesteric liquid crystal(CLC) layers described according to various embodiments described above.

Still referring to FIG. 25A, in the following, the display device 2500Ais further described in operation. As described above, some of the lightpropagating in the x-direction within one or more waveguides within thewaveguide assembly 2504 may be redirected, or out-coupled, in thez-direction. In the illustrated embodiment, the light out-coupled fromthe waveguide assembly 2504 includes a circularly polarized light beams2516-L having LHCP and 2516-R having RHCP. The light beams 2516-L havingLHCP and 2516-R having RHCP travel, e.g., in a positive z-direction,until the beams impinge on a surface of the polarizing notch reflector2512.

The polarizing notch reflector 2512 comprises a CLC layer 1004 havingchiral structures similar to those described above, e.g., chiralstructures 1012-1, 1012-2, . . . 1012-i described above with respect toFIG. 10. In operation, when incident light having a combination of lightbeams having left-handed circular polarization and light beams havingright-handed circular polarization are incident on the surface of thepolarizing notch reflector 2512, by Bragg-reflection, light with one ofthe circular polarization handedness is reflected by the CLC layer 1004,while light with the opposite polarization handedness is transmittedthrough the CLC layer 1008 without substantial interference. Asdescribed herein and throughout the disclosure, the handedness isdefined as viewed in the direction of propagation. According toembodiments, when the direction of polarization, or handedness of thepolarization, of the light beams 2516-L, 2516-R is matched such that itand has the same direction of rotation as the liquid crystal moleculesof the chiral structures 1012-1, 1012-2, . . . 1012-i, the incidentlight is reflected. As illustrated, incident on the surface of the CLClayer 1004 are light beams 2516-L having left-handed circularpolarization and light beams 2516-R having a right-handed circularpolarization. In the illustrated embodiment, the liquid crystalmolecules of the chiral structures 1012-1, 1012-2, . . . 1012-i arerotated in a clockwise direction successively in the direction in whichincident light beams 2516-L, 2516-R travel, e.g., positive x-direction,which is the same rotation direction as the light teams 1016-L havingleft-handed circular polarization. As a result, the light beam 2516-Lhaving right-handed circular polarization is substantially reflected offthe polarizing notch reflector 2512, whereas the light beam 2516-Rhaving right-handed circular polarization is substantially transmittedthrough the polarizing notch reflector 2512.

The light beam 2516-L out-coupled from the CLC layer 1004 and havingLHCP is reflected by the polarizing notch reflector 2512 as a light beam2520-L, which retains the same polarization as the light beam 2516-L.The resulting light beam 2520-L propagates toward the non-polarizingnotch reflector 2508 until the light beam 2520-L, which has LHCP, issubstantially reflected by the non-polarizing notch reflector 2508 intoa light beam 2520-R having the opposite polarization handedness, e.g.,RHCP, due to the polarization-converting characteristics of thenon-polarizing notch reflector 2508. The resulting light beam 2520-Rhaving RHCP is substantially transmitted through the CLC layer 1004 andfurther through the polarizing notch reflector 2512 to enter the eye 4.Still referring to FIG. 25A in summary, by disposing the polarizingnotch reflector 2512 (e.g., a cholesteric liquid crystal (CLC) notchreflector) between the waveguide assembly 2504 and the user's eye 4,light beam 2516-R having one polarization (e.g., right-handed circularpolarization (RHCP)) is transmitted through the polarizing notchreflector 2512 while light 2516-L having an orthogonal polarization(e.g., left-handed circular polarization (LHCP)) is reflected toward theworld 1114 as the light beam 2520-L. Another notch reflector, thenon-polarizing notch reflector 2508 (e.g., multi-layer notch reflector),is disposed between the world 1114 and the waveguide assembly 2504 andconfigured to reflect the light beam 2520-L back to the user's eye asthe light beam 2520-R. Since the polarizing notch reflector 2512, e.g.,a CLC notch reflector, does not convert the polarization of lightreflected therefrom, whereas the non-polarizing notch reflector, e.g., amulti-layer reflector, does convert the polarization of light reflectedtherefrom, the light beam 2516-R can also be transmitted through thepolarizing notch reflector 2512 as shown. It will be appreciated thatboth notch reflectors 2512, 2508 (e.g., CLC and multi-layer) can bedesigned to reflect only light sources for virtual images to minimizeeffects on images of the world 1114.

Example Linear Polarization Converting Display Devices

FIG. 25B illustrates a display device 2500B configured to output imageinformation to a user. Similar to the display device 2500A illustratedabove with respect to FIG. 25A, the display device 2500B comprises awaveguide assembly 2504 interposed between a non-polarizing notchreflector 2508 and a polarizing notch reflector 2514, e.g., a linearpolarizing notch reflector. The waveguide assembly 2504 and thenon-polarizing notch reflector 2508 are configured in a similar manneras described above with respect to FIG. 25A, and therefore are notdescribed in detail herein.

Still referring to FIG. 25B, similar to the polarizing notch reflector2512 described above with respect to FIG. 25A, the polarizing notchreflector 2514 in the illustrated embodiment is configured such that,within the notch-reflective range, the notch reflector 2514substantially reflects light incident thereon in apolarization-selective manner. Furthermore, in the illustratedembodiment, the polarizing reflector 2514 is configured such that,unlike the non-polarizing notch reflector 2508, the polarizing reflector2514 does not convert the polarization of the reflected light to anopposite polarity.

However, unlike the polarizing notch reflector 2512 described above withrespect to FIG. 25A the polarizing notch reflector 2514 in theillustrated embodiment is configured such that the polarizing notchreflector 2514 does not include a CLC layer. Instead, the polarizingnotch reflector 2514 includes a transmissive substrate, e.g., a polishedglass or polymer substrate, having formed thereon one or more activelayers. In some embodiments of the notch reflectors described herein,the one or more active layers formed on a substrate can include one ormore dielectric coatings, whose combination gives rise to the variousnotch-reflective characteristics described above.

Still referring to FIG. 25B, the display device 2500B further comprisesa quarter-wave plate 2510 interposed between the non-polarizing notchreflector 2508 and the waveguide assembly 2504.

Still referring to FIG. 25B, in the following, the display device 2500Bis further described in operation. As described above, some of the lightpropagating in the x-direction within one or more waveguides within thewaveguide assembly 2504 may be redirected, or out-coupled, in thez-direction. In the illustrated embodiment, the light out-coupled fromthe waveguide assembly 2504 includes linearly polarized light beams2516-V having LVP and 2516-H having LHP. The light beams 2516-V havingLVP and 2516-H having LHP travel, e.g., in a positive z-direction, untilthe beams impinge on a surface of the polarizing notch reflector 2514.Thereupon, the light beam 2516-V having LVP is substantially reflectedoff the polarizing notch reflector 2514, whereas the light beam 2516-Hhaving LHP is substantially transmitted through the polarizing notchreflector 2514.

The light beam 2516-V out-coupled from the waveguide assembly 2504 andhaving LVP is reflected by the polarizing notch reflector 2514 as alight beam 2520-V, which retains the same polarization as the light beam2516-V. The resulting light beam 2520-V, which has LVP, propagatestoward and is transmitted through the quarter-wave plate 2510, to bereflected off of the non-polarizing notch reflector 2508 and furthertransmitted through the quarter-wave plate 2510 as a light beam 2520-Hhaving the opposite polarization handedness, e.g., LHP, due to thepolarization-converting characteristics of the non-polarizing notchreflector 2508. The resulting light beam 2520-H having LHP issubstantially transmitted through the polarizing notch reflector 2514.

Still referring to FIG. 25B in summary, by disposing the polarizingnotch reflector 2514, which reflects one linear polarization (e.g.,linear vertical polarization (LVP)) for specific wavelengths, instead ofa CLC-containing polarizing notch reflector 2512 (FIG. 25A), and furtherdisposing a quarter-wave plate 2510 interposed between thenon-polarizing notch reflector 2508 and the waveguide assembly 2504, thepolarization of the light reflected off the non-polarizing notchreflector 2508 becomes orthogonal (e.g., linear horizontal polarization(LHP)) as shown. Similar to the CLC-containing notch reflector describedabove with respect to FIG. 25A, the polarization of the projectedvirtual image is converted into one linear polarization in an efficientmanner (e.g., close to 100% efficiency).

Variable-Focus Virtual Imaging Systems Based on Polarization Converters

Example Linear Polarization Variable-Focus Lenses

FIGS. 26A and 26B illustrate display devices 2600A, 2600B configured tooutput image information to a user. The display devices 2600A and 2600Bare structurally identical. The display device 2600A is used herein todescribe outputting virtual image to the user, while the display device2600B is used herein to describe outputting real world image to theuser.

The display device 2600A/2600B comprises various components of thedisplay device 2500A described above with respect to FIG. 25A, andfurther includes additional optical components for focusing andconverting the light output therefrom. Similar to the display device2500A illustrated above with respect to FIG. 25A, the display device2600A/2600B comprises a waveguide assembly 2504 interposed between anon-polarizing notch reflector 2508 and a polarizing notch reflector2512. The waveguide assembly 2504, the non-polarizing notch reflector2508 and the polarizing notch reflector 2512 are configured in a similarmanner as described above with respect to FIG. 25A, and therefore arenot described in further detail herein.

The display device 2600A/2600B additionally includes a firstquarter-wave plate (QWP 1) 2604 and a second quarter-wave plate (QWP 2)2608 formed on outer sides of the non-polarizing notch reflector 2508,e.g., a multilayer notch reflector, and the polarizing notch reflector2512, e.g., a CLC notch reflector, and further includes a first linearpolarizing lens (L1) 2612 and a second linear polarizing lens (L2) 2616formed on outer sides of the QWP 1 2504 and QWP 2 2608. In variousembodiments, one or both of the L and L2 can be switchable lenses, whichcan be switchable by e.g., application of an electric field, a voltageor a current. Further, one or both of the L1 and L2 can have variablefocal strengths or focal depths, whose focal strengths and focal depthscan be controlled, e.g., by application of application an electricfield, a voltage or a current.

Referring to FIG. 26A, the display device 2600A is used herein todescribe outputting virtual image to the user. As described above withrespect to FIG. 25A, some of the light propagating in the x-directionwithin one or more waveguides within the waveguide assembly 2504 may beredirected, or out-coupled, in the z-direction. In the illustratedembodiment, the light out-coupled from the waveguide assembly 2504includes a circularly polarized light beams 2516-L having LHCP and2516-R having RHCP. The light beams 2516-L having LHCP and 2516-R havingRHCP travel, e.g., in a positive z-direction, until the beams impinge ona surface of the polarizing notch reflector 2512. Because of the CLClayer 1004 included in the polarizing notch reflector 2512, the lightbeam 2516-L having right-handed circular polarization is substantiallyreflected off the polarizing notch reflector 2512, whereas the lightbeam 2516-R having right-handed circular polarization is substantiallytransmitted through the polarizing notch reflector 2512.

The light beam 2516-L out-coupled from the CLC layer 1004 and havingLHCP is reflected by the polarizing notch reflector 2512 as a light beam2520-L, which retains the same polarization as the light beam 2516-L.The resulting light beam 2520-L propagates toward the non-polarizingnotch reflector 2508 until the light beam 2520-L, which has LHCP, issubstantially reflected by the non-polarizing notch reflector 2508 intoa light beam 2520-R having the opposite polarization handedness, e.g.,RHCP, due to the polarization-converting characteristics of thenon-polarizing notch reflector 2508. The resulting light beam 2520-Rhaving RHCP is substantially transmitted through the polarizing notchreflector 2512 having the CLC layer 1004.

Upon exiting the polarizing notch reflector 2512, the light beams 2516-Rand 2520-R having RHCP are further transmitted through the QWP2 2608,which converts the circularly polarized light beams 2516-R and 2520-Rinto linearly polarized light beams 2520-H and 2516-H, respectively.Thereafter, upon exiting the QWP2 2608, the light beams 2520-H and2516-H are further transmitted through the L2 2616. When activated, theL2 2616 focuses or defocuses the light beams 2520-H and 2516-H intofocused output light beams 2620, prior to being viewed by the eye 4.

In summary, the illustrated embodiment of FIG. 26A shows one example ofa waveguide-based projection display having with variablefocus/switchable lenses, which are configured to operate on light havinglinear polarization (e.g., LHP in the illustrated embodiment). Thus thepolarization of light of the virtual images is converted to have one ofcircular polarizations (e.g., RHCP in FIG. 26A) as the light passesthrough the polarizing notch reflector 2512, e.g., a CLC notchreflector, and further converted to have one of linear polarizations(e.g., LHP in FIG. 26A) by the QWP2 2608. The focus of the virtual imageis controlled by the L2 2616, as shown in FIG. 26A.

Referring to FIG. 26B, the display device 2600B is used herein todescribe outputting an image of the world 1114 to the user. Asillustrated, incident light beams 2632-H and 2624-V having LHP and LVP,respectively, enter and are transmitted through L1 2612. Upon exiting L12612, the light beams 2632-H and 2624-V pass through the QWP1 2604,which converts the respective light beams into light beams 2632-R and2624-L having RHCP and LHCP, respectively. The light beams 2632-R and2624-L are subsequently transmitted through nonpolarizing notchreflector 2508, the waveguide assembly 2504, the polarizing notchreflector 2512 and QWP2 2608, thereby re-converting the respective lightbeams into light beams 2636-H and 2628-V having LHP and LVP,respectively. Thereafter, the light beams 2636-H and 2628-V aretransmitted through the L2 2616, thereby outputting the respective lightbeams 2636 and 2628, respectively.

For outputting a real-world image, the lenses L1 2612 and L2 2616 areconfigured to operate on light having one of the linear polarization butnot the other. As a result, in the illustrated embodiment, one of theincident light beams 2632-H and 2624-V, e.g., the light beam 2632-Hhaving the LHP, is not affected by lenses L1 2612 and L2 2616.

The L1 2612 and the L2 2616 can be configured to have opposite lensingeffects or optical powers on light passing therethrough. For example, ifthe L1 2612 is configured to have a focusing lensing effect, the L2 2616can be configured to have a defocusing effect such that the oppositelensing effects negate each other. Thus, the other of the incident lightbeams 2632-H and 2624-V, e.g., the light beam 2632-V having LVP,undergoes a lensing effect, e.g., focusing or defocusing, by the L1 2612upon passing therethrough. However, after being converted to the lightbeam 2624-L having LHCP and back converted to the light beam 2628-Vhaving LVP, the lensing effect of the L1 2612 is negated by the L2 2616having the opposite lensing effect. Thus, because there are the twoquarter-wave plates QWP1 2604, QWP2 2608 whose light retardation effectsnegate each other, and because there are two lenses L1 2612 and the L22616 whose lensing effects negate each other, the image of the world1114 as viewed by the eye 4 can be substantially unaffected, while thevirtual image is affected by the L2 2616, as described above withrespect to FIG. 26B.

As described above, polarization conversion similar to that performedusing the display device 2500A (FIG. 25A) having a polarizing notchreflector 2512, which includes a CLC layer 1004, can also be performedusing the display device 2500B (FIG. 25B) having a polarizing notchreflector 2514 that does not include a CLC layer. Accordingly, FIGS. 26Cand 26D illustrate display devices 2600C, 2600D configured to outputimage information to a user, where the display devices 2600C, 2600D havea polarizing notch reflector 2514 that does not include a CLC layer. Thedisplay devices 2600C and 2600D are structurally identical. The displaydevice 2600C is used herein to describe outputting virtual image to theuser, while the display device 2600D is used herein to describeoutputting real world image to the user.

Similar to the display device 2500B illustrated above with respect toFIG. 25B, the display device 2600C/2600D comprises a waveguide assembly2504 interposed between a non-polarizing notch reflector 2508 and apolarizing notch reflector 2514. The waveguide assembly 2504 and thenon-polarizing notch reflector 2508 are configured in a similar manneras described above with respect to FIG. 25A, and therefore are notdescribed in further detail herein.

Still referring to FIG. 26C, in a similar manner as described above withrespect to FIG. 25B, the polarizing notch reflector 2514 in theillustrated embodiment is configured such that, within thenotch-reflective range, the notch reflector 2514 substantially reflectslight incident thereon in a polarization-selective manner. Furthermore,in the illustrated embodiment, the polarizing reflector 2514 isconfigured such that, unlike the non-polarizing notch reflector 2508,polarizing reflector 2514 does not convert the polarization of thereflected light to an opposite polarity.

Still similar to the description above with respect to FIG. 25B, thepolarizing notch reflector 2514 of the display device 2600C/2600D in theillustrated embodiment is configured such that the polarizing notchreflector 2514 does not include a CLC layer. In addition, the displaydevice 2600C/2600D further comprises a second quarter-wave plate QWP12510 interposed between the non-polarizing notch reflector 2508 and thewaveguide assembly 2504.

The display device 2600C/2600D additionally includes a firstquarter-wave plate (QWP 1) 2604 formed on the left side (the side of theworld 1114) of the non-polarizing notch reflector 2508, e.g., amultilayer notch reflector, and further includes a first linearpolarizing lens (L1) 2612 and a second linear polarizing lens (L2) 2616formed on outer sides of the QWP 1 2504 and the polarizing notchreflector 2514, respectively. In various embodiments, one or both of theL1 and L2 can be switchable lenses, which can be switchable by e.g.,application of an electric field, a voltage or a current. Further, oneor both of the L1 and L2 can have variable focal strengths or focaldepths, whose focal strengths and focal depths can be controlled, e.g.,by application of application an electric field, a voltage or a current.

Referring to FIG. 26C, the display device 2600C is used herein todescribe outputting virtual image to the user. As described above withrespect to FIG. 25B, some of the light propagating in the x-directionwithin one or more waveguides within the waveguide assembly 2504 may beredirected, or out-coupled, in the z-direction. In the illustratedembodiment, the light out-coupled from the waveguide assembly 2504includes linearly polarized light beams 2516-V having LVP and 2516-Hhaving LHP. The light beams 2516-V having LVP and 2516-H having LHPtravel, e.g., in a positive z-direction, until the beams impinge on asurface of the polarizing notch reflector 2514. Thereupon, the lightbeam 2516-V having LVP is substantially reflected off the polarizingnotch reflector 2514, whereas the light beam 2516-H having LHP issubstantially transmitted through the polarizing notch reflector 2514.

The light beam 2516-V out-coupled from the waveguide assembly 2504 andhaving LVP is reflected by the polarizing notch reflector 2514 as alight beam 2520-V, which retains the same polarization as the light beam2516-V. The resulting light beam 2520-V, which has LVP, propagatestoward and is transmitted through the QWP2 2510, to be reflected off ofthe non-polarizing notch reflector 2508 and further transmitted throughthe QWP2 2510 as a light beam 2520-H having the opposite polarizationhandedness, e.g., LHP, due to the polarization-convertingcharacteristics of the non-polarizing notch reflector 2508. Theresulting light beam 2520-H having LHP is substantially transmittedthrough the polarizing notch reflector 2514.

Upon exiting the polarizing notch reflector 2514, the light beams 2516-Vand 2516-H having LHP are further transmitted through the L2 2616. Whenactivated, the L2 focuses or defocuses the light beams 2520-H and 2516-Hinto focused output light beams 2620, prior to being viewed by the eye4.

Referring to FIG. 26D, the display device 2600D is used herein todescribe outputting an image of the world 1114 to the user. Asillustrated, incident light beams 2632-H and 2624-V having LHP and LVP,respectively, enter and are transmitted through L1 2612. Upon exiting L12612, the light beams 2632-H and 2624-V pass through the QWP1 2604,which converts the respective light beams into light beams having RHCPand LHCP, respectively. The light beams 2632-R and 2624-L aresubsequently transmitted through nonpolarizing notch reflector 2508,followed by the QWP2 2510, which back-converts the light beams havingRHCP and LHCP into light beams 2636-H and 2628-V having LHP and LVP,respectively. Thereafter, the light beams 2636-H and 2628-V aretransmitted through the waveguide assembly 2504, followed by thepolarizing notch reflector 2514, followed by L2 2616, thereby outputtingthe respective light beams 2636 and 2628, respectively.

Similar to the display device described above with respect to FIGS.26A/26B, the lenses L1 2612 and L2 2616 are configured to operate onlight having one of the linear polarization but not the other. As aresult, in the illustrated embodiment, one of the incident light beams2632-H and 2624-V, e.g., the light beam 2632-H having LHP, is notaffected by lenses L1 2612 and L2 2616.

Also similar to the display device described above with respect to FIGS.26A/26B, because there are the two quarter-wave plates QWP1 2604, QWP22608 whose light retardation effects negate each other, and becausethere are two lenses L1 2612 and the L2 2616 whose lensing effectsnegate each other, the image of the world 1114 as viewed by the eye 4 issubstantially unaffected, while the virtual image is affected by the L22616, as described above with respect to FIG. 26C.

In summary, the embodiment illustrated in FIGS. 26C and 26D,polarization conversion similar to that achieved using the displaydevice 2600A/2600B having polarizing notch reflectors comprising CLClayers therein can be achieved using a polarizing notch reflector 2514,e.g., a linear polarizing notch reflector, in lieu of a polarizing notchreflector 2514 (FIGS. 26A/26B) having CLC layers therein, as shown inFIGS. 26C and 26D. To convert the polarization of virtual images, theQWP2 2510 is disposed between the non-polarizing notch reflector 2508and the waveguide assembly 2504. Since the polarizing notch reflector2514, e.g., a linear polarizing notch reflector, converts virtual imagepolarization to a linear polarization (e.g., LHP), another quarter-waveplate QWP1 2604 is disposed between the L1 2612 and the non-polarizingnotch reflector 2508 to compensate.

Example Circular Polarization Variable-Focus Lenses

Without being bound to any theory, when a light beam is taken along aclosed cycle in the space of polarization states of light, it mayacquire a dynamic phase from the accumulated path lengths as well asfrom a geometric phase. The dynamic phase acquired from a geometricphase is due to local changes in polarization. In contrast, some opticalelements based on a geometric phase to form a desired phase front may bereferred to as Pancharatnam-Berry phase optical elements (PBOEs). PBOEsmay be constructed from wave plate elements for which the orientation ofthe fast axes depends on the spatial position of the waveplate elements.Applications of the PBOEs include diffraction gratings, e.g., blazedgratings, focusing lenses, and axicons, among various otherapplications.

In the following, with respect to FIGS. 27A-27D, display devicesemploying switchable lens elements or a switchable lens assemblyincluding, e.g., Pancharatnam-Barry phase (PB) lens elements, which canbe dynamically switched by direct modulation of a PB lens or bymodulation of LC waveplates coupled to a static PB lens, are described.When multiple PB lens elements with different focal distances arestacked, the overall focus of the lens stack can be switched among themby modulating the PB lens or LC waveplates placed between them.Advantageously, PB lenses can be configured to focus or defocus lighthaving circular polarization. As a result, quarter-wave plate(s)included as part of display devices, e.g., display devices 2600A, 2600B,can be omitted as the virtual image polarization is converted to acircular polarization (e.g., RHCP) through the CLC reflector.

FIGS. 27A and 27B illustrate display devices 2700A, 2700B configured tooutput image information to a user. The display devices 2700A and 2700Bare structurally identical. The display device 2700A is used herein todescribe outputting virtual image to the user, while the display device2700B is used herein to describe outputting real world image to theuser.

The display device 2700A/2700B comprises various components of thedisplay device 2600A/2600B described above with respect to FIGS. 26A and26B, and further includes additional optical components for focusing andconverting the light output therefrom. Similar to the display device2600A/2600B illustrated above with respect to FIGS. 26A and 26B, thedisplay device 2700A/2700B comprises a waveguide assembly 2504interposed between a non-polarizing notch reflector 2508 and apolarizing notch reflector 2512. The waveguide assembly 2504, thenon-polarizing notch reflector 2508 and the polarizing notch reflector2512 are configured in a similar manner as described above with respectto FIGS. 26A and 26B, and therefore are not described in further detailherein.

Unlike the display device 2600A/2600B, however, in the display device2700A/2700B, quarter-wave plates formed on outer sides of thenon-polarizing notch reflector 2508, e.g., a multilayer notch reflector,and the polarizing notch reflector 2512, e.g., a CLC notch reflector,are omitted. Further unlike the display device 2600A/2600B, instead oflinear polarization lenses, the display device 2700A/2700B includes afirst PB lens (PB L1) 2712 and a second PB lens (PB L2) 2716 formed onouter sides of the non-polarizing notch reflector 2508 and thepolarizing notch reflector 2512, respectively. In various embodiments,one or both of the PB L1 2712 and PB L2 2716 can be switchable lenses,which can be switchable by e.g., application of an electric field, avoltage or a current. Further, one or both of the PB L1 2712 and PB L22716 can have variable focal strengths, optical power or focal depths,which can be controlled, e.g., by application of an electric field, avoltage or a current.

Referring to FIG. 27A, the display device 2700A is used herein todescribe outputting virtual image to the user. In operation, the asdescribed above with respect to FIG. 25A, some of the light propagatingin the x-direction within one or more waveguides within the waveguideassembly 2504 may be redirected, or out-coupled, in the z-direction. Thepaths of light beams out-coupled from the waveguide assembly 2504, whichincludes a circularly polarized light beams 2516-L having LHCP and2516-R having RHCP, are the same as those described above with respectto FIG. 26A until the light beams 2516-R and 2520-R having RHCP aretransmitted through the polarizing notch reflector 2512 having the CLClayer 1004. Upon exiting the polarizing notch reflector 2512, the lightbeams 2516-R and 2520-R having RHCP are further transmitted through thePB L2 2716. When activated, the PB L2 focuses or defocuses the lightbeams 2520-H and 2516-H into focused output light beams 2620, prior tobeing viewed by the eye 4.

Referring to FIG. 27B, the display device 2700B is used herein todescribe outputting an image of the world 1114 to the user. Asillustrated, incident light beams 2632-R and 2624-L having RHCP andLHCP, respectively, are transmitted through the PB L1 2712 as lightbeams 2636-R and 2628-L that are subsequently transmitted through thenonpolarizing notch reflector 2508, the waveguide assembly 2504, thepolarizing notch reflector 2512 and PB L2 2716. Unlike the displaydevice 2600B illustrated above with respect to FIG. 26B, because thereare no quarter-wave plates in the display device 2700, the light beamsremain as circularly polarized light beams throughout the phaseconversion and focusing. Thereafter, the light beams 2636-R and 2628-Lare transmitted through the PB L2 2716, thereby outputting therespective light beams 2632 and 2628, respectively.

For outputting a real-world image, the lenses PB L1 2712 and PB L2 2716are configured to operate on light having one of the circularpolarization but not the other. As a result, in the illustratedembodiment, one of the incident light beams 2632-R and 2624-L, e.g., thelight beam 2624-L having the LHCP, is not affected by lenses PB L1 2712and PB L2 2716.

The PB L1 2712 and the PB L2 2716 can be configured to have oppositelensing effects on light passing therethrough. For example, if the PB L12712 is configured to have a focusing lensing effect, the PB L2 2716 canbe configured to have a defocusing effect such that the opposite lensingeffects negate each other. As a result, the image of the world 1114 asviewed by the eye 4 is substantially unaffected, while the virtual imageis affected by the PB L2 2716, as described above with respect to FIG.27A.

As described above, polarization conversion similar to that performedusing the display device 2500A (FIG. 25A) having a polarizing notchreflector 2512, which includes a CLC layer 1004, can also be performedusing the display device 2500B (FIG. 25B) having a polarizing notchreflector 2514 that does not include a CLC layer. Accordingly, FIGS. 27Cand 27D illustrate display devices 2700C, 2700D configured to outputimage information to a user, where the display devices 2700C, 2700D havea polarizing notch reflector 2514 that does not include a CLC layer. Thedisplay devices 2600C and 2600D are structurally identical. The displaydevice 2700C is used herein to describe outputting virtual image to theuser, while the display device 2700D is used herein to describeoutputting real world image to the user.

Similar to the display device 2500B illustrated above with respect toFIG. 25B, the display device 2700C/2700D comprises a waveguide assembly2504 interposed between a non-polarizing notch reflector 2508 and apolarizing notch reflector 2514. The waveguide assembly 2504 and thenon-polarizing notch reflector 2508 are configured in a similar manneras described above with respect to FIG. 25A, and therefore are notdescribed in further detail herein.

The display device 2700C/2700D additionally includes a firstquarter-wave plate (QWP 1) 2604 formed between the non-polarizing notchreflector 2508, e.g., a multilayer notch reflector, and the waveguideassembly 2504, and a second quarter-wave plate (QWP2) 2510 formedbetween the polarizing notch reflector 2514 and a second PB lens (PB L2)2616. The display device 2700C/2700D further includes a first PB lens(PB L) 2612 on an outer sides of the non-polarizing notch reflector2508. Thus, the display device 2700C/2700D is similar to the displaydevice 2600C/2600D described with respect to FIGS. 26C and 27D exceptfor the relative positions of the QWP1 2604 and QWP2510 and the type oflenses.

In various embodiments, one or both of the PB L1 2612 and PB L2 2616 canbe switchable lenses, which can be switchable by e.g., application of anelectric field, a voltage or a current. Further, one or both of the PBL1 2612 and PB L2 2616 can have variable focal strengths or focaldepths, whose focal strengths and focal depths can be controlled, e.g.,by application of application an electric field, a voltage or a current.

Referring to FIG. 27C, the display device 2700C is used herein todescribe outputting virtual image to the user. As described above withrespect to FIG. 25B, some of the light propagating in the x-directionwithin one or more waveguides within the waveguide assembly 2504 may beredirected, or out-coupled, in the z-direction. The paths of light beamsout-coupled from the waveguide assembly 2504, which includes linearlypolarized light beams 2516-V having LVP and 2516-H having LHP, are thesame as those described above with respect to FIG. 26C until the lightbeams 2516-V and 2520-V having LVP are transmitted through thepolarizing notch reflector 2514, e.g., a linear polarizing notchreflector. Upon exiting the polarizing notch reflector 2514, the lightbeams 2516-V and 2520-V are transmitted through the QWP2 2510, therebybeing converted to light beams 2516-R and 2520-R having RHCP.Thereafter, the light beams 2516-R and 2520-R having RHCP are furthertransmitted through the PB L2 2716. When activated, the PB L2 focuses ordefocuses the light beams 2520-R and 2516-R into focused output lightbeams 2620, prior to being viewed by the eye 4.

Referring to FIG. 27D, the display device 2700D is used herein todescribe outputting an image of the world 1114 to the user. Asillustrated, incident light beams 2632-R and 2624-L having RHCP andLHCP, respectively, are transmitted through the PB L1 2712, through thenonpolarizing notch reflector 2508, and through the QWP1 2604, whereuponthe light beams are converted to linear polarized light beams. Thecircular polarized light beams are further transmitted though thewaveguide assembly 2504, the polarizing notch reflector 2514, e.g., alinear polarizing notch reflector, and through the QWP2 2510, whereuponthe light beams are back-converted to circular polarized light beams2636-R and 2628-L having RHCP and LHCP, respectively. Thereafter, thelight beams 2636-R and 2628-L are transmitted through the PB L2 2716,thereby outputting the respective light beams 2632 and 2628,respectively.

For outputting a real-world image, the lenses PB L1 2712 and PB L2 2716are configured to operate on light having one of the circularpolarization but not the other. As a result, in the illustratedembodiment, one of the incident light beams 2632-R and 2624-L, e.g., thelight beam 2624-L having the LHCP, is not affected by lenses PB L1 2712and PB L2 2716.

The PB L1 2712 and the PB L2 2716 can be configured to have oppositelensing effects on light passing therethrough. For example, if the PB L12712 is configured to have a focusing lensing effect, the PB L2 2716 canbe configured to have a defocusing effect such that the opposite lensingeffects negate each other. As a result, the image of the world 1114 asviewed by the eye 4 is substantially unaffected, while the virtual imageis affected by the PB L2 2716, as described above with respect to FIG.27C.

Example Spatial Offset Compensators for Polarization-SensitiveVariable-Focus Lenses

When a polarization-sensitive lens such as a PB lens is used, twoorthogonal polarization images undergo different optical passes throughlenses. For example, a PB lens can split the world-image into twopolarization images having different magnifications (which can lead todouble images with a spatial offset between them). This effect isillustrated in FIG. 28A, which illustrates a display device 2800Aconfigured similarly as the display device 2700A/2700B of FIGS. 27A and27B. As described above, while two PB lenses can be configured tonegates the lens effect of each other, an offset 2804 in the sizes oftwo polarization images formed by the light beam 2632 having LHCP and bythe light beam 2628 having RHCP may remain, as illustrated in FIG. 28A.For example, in FIG. 28A, the PB L1 exerts a negative optical power onthe light beam 2624-L having LHCP, while exerting a positive opticalpower on the light beam 2632-R having RHCP. In the following, variousarrangements configured to compensate the offset 2804 are disclosed.

FIG. 28B illustrates an offset compensator 2800B comprising a pair oflenses 2804, 2808, e.g., a pair of PB lenses. The pair of lenses PB L32804 and PB L4 2808 are configured such that, when incident light beamshaving RHCP and LHCP are incident on the PB L3, the PB L3 exerts apositive optical power on the light beam having LHCP, while exerting anegative optical power on the light beam having RHCP. Thus, the opticalpowers of PB L3 2804 and P L4 2808 are opposite to those of PB L1 2612and PB L2 2716, respectively, such that a spatial offset 2812 is presentbetween the output light beams 2632 and 2628 output from the displaydevice 2800A (FIG. 28A), which is opposite in direction andsubstantially the same in magnitude compared to output light beams 2632and 2628 output from the offset compensator 2800B. Thus, the spatialoffset 2804 illustrated in FIG. 28A can be compensated by placing a pairof lenses that produce an offset 2812 having the same magnitude in theopposite direction, as illustrated in FIG. 28B.

FIG. 28C illustrates a combination of the display device 2800A (FIG.28A) stacked with the offset compensator 2800B (FIG. 28B). Same types ofvariable focus lenses as used in the optics of FIG. 28A can be used toconstruct the offset compensator. Static lenses can be used when apartial compensation is acceptable. As illustrated, the offset can beavoided by placing a polarizer in the front of the notch filter (e.g.,linear polarizer for linear LC lenses or circular polarizer for PBlenses) while sacrificing brightness of the world image. Still, thevirtual image is not affected. The offset compensator 2800B can bedisposed world-ward of the eyepiece (e.g., as shown in FIG. 28C) or canbe disposed eye-ward of the eyepiece (e.g., toward the right, where theuser's eye is located). Multiple offset compensators can be used.

As described above with respect to various display devices, lightpropagating generally in a propagation direction, e.g., the x-direction,within one or more waveguides (e.g., 1182, 1184, 1186, 1188, 1190 inFIG. 6) in a waveguide assembly 2504 may be output, e.g., usingout-coupling optical elements or light extracting optical elements(e.g., 1282, 1284, 1286, 1288, 1290 in FIG. 6), out of the waveguides,to output image information in an orthogonal direction, e.g., thez-direction. As described above, various embodiments of the out-couplingoptical elements may comprise cholesteric liquid crystal gratings(CLCGs). As the light propagate within the one or more waveguides (e.g.,1182, 1184, 1186, 1188, 1190 in FIG. 6) the CLCGs (e.g., 1282, 1284,1286, 1288, 1290 in FIG. 6) couple light out of the one or morewaveguides. Under some configurations of the CLC layers of the CLCGs,the out-coupled light can have uniform polarization state insubstantially a single direction, e.g., the z-direction. For example,the CLC layer(s) of CLCGs having chiral structures (e.g., 1012-1,1012-2, . . . 1012-i in FIG. 10), in which the liquid crystal moleculesare rotated in the same direction, e.g., clockwise or counter-clockwisedirection, may out-couple light having substantially uniformpolarization, e.g., LHCP or RHCP. In these embodiments, because thewaveguide assembly 2504 out-couples light having substantially uniformpolarization, a display device incorporating a waveguide assembly 2504comprising CLCGs may omit some of the optical elements described abovefor converting the polarization of the output light.

Example Polarization Eyepieces with Variable-Focus Lenses

In the following, the eye-piece 1004 may preferentially project light ina particular direction (e.g., to the right, eye-ward, in FIG. 29) ascompared to other directions (e.g., to the left, world-ward, in FIG.29). Referring to FIG. 29, a display device 2900 comprises the waveguideassembly 2904, where the waveguide assembly 2904 is interposed betweenfirst and second PB lenses 2612 and 2616, respectively. Advantageously,in this example, since the light beam 2636-R of the image output fromthe waveguide assembly 2904 is already polarized (e.g., right-handedcircular polarization or RHCP), additional polarizer or polarizationconversion may be omitted, because the light projected from the eyepiece1004 is already preferentially in the polarization state (RHCP in thisexample) that is acted on by the lens 2616. Thus, some of the lightpropagating under TIR in the waveguide assembly 2904 may be out-coupledby DOEs formed therein as, for example, circularly polarized light beam2636-R (or linearly polarized light beams in other implementations). Thelight beams 2636-R having RHCP travel, e.g., in a positive z-direction,until the beams impinge on the PB L2 2616 without passing through apolarizing notch reflector before being viewed by the eye 4. Theeyepiece 1004 may include DOEs, metamaterials, holograms that aredesigned to asymmetrically project light in the desired direction and(optionally) with the desired polarization state (e.g., in FIG. 29, tothe right with RHCP).

Example Deformable Mirror Variable-Focus Displays

In some embodiments, a deformable mirror can be used to make variablefocus effects on virtual images when it is reflected from a mirror. FIG.30 illustrates a display device 3000 configured to output imageinformation to a user using a waveguide assembly 2904 and a deformablemirror 3004. The display device 3000 comprises a waveguide assembly2904, where the waveguide assembly 2904 is interposed between a curvedor deformable mirror 3004 (so that it has optical power) and an optionalclean-polarizer 3008. As described with reference to FIG. 29, theeyepiece 2904 may be configured to asymmetrically project light, in thisexample, toward the left (world-ward) rather than to the right(eye-ward). The eyepiece 2904 may comprise DOEs, metamaterials,holograms, etc. that can preferentially project light in the desired,asymmetric direction and/or desired polarization state (e.g., linear orcircular). For example, as shown in FIG. 34, the eyepiece 2904 maycomprise a CLC layer or CLCG.

In operation, as described above with respect to FIG. 29, some of thelight propagating in the x-direction within one or more waveguideswithin the waveguide assembly 2904 may be redirected, or out-coupled, inthe z-direction as a light beam 3012 having a uniform circularpolarization (e.g., RHCP). The waveguide assembly 2904 projects thelight beam 3012 of a virtual image toward the curved or deformablemirror 3004 (in the opposite to side of the user's eye 4). In someembodiments, the deformable mirror 3004 is coated with a polarizingreflection layer (e.g., multi-layer linear polarization reflectors orbroadband cholesteric liquid crystal circular polarization reflectors)to reflect light having a designated polarization, e.g., light havingthe same polarization as the out-coupling polarization of the CLCGs, andto allow light from the real world 1114 transmitted toward the eye 4. Insome other embodiments, instead of a polarizing reflection layer, thedeformable mirror 3004 is coated with a notch reflection layer or CLCreflection layer, which is designed to reflect light within a narrowbandwidth Δλ that matches the virtual image bandwidth of the out-coupledlight from the waveguide assembly 2904. In some embodiments, a clean-uppolarizer 3008 can optionally be placed as shown in FIG. 30 to eliminateany ghost images without going through the deformable mirror.

Cholesteric Liquid Crystal Lenses

As described elsewhere herein (see, e.g., FIGS. 30 and 34), some displaydevices comprise an eyepiece configured to asymmetrically project lightworld-ward (e.g., away from the user's eye 4 toward the world 1114) andthen an optical structure (e.g., the deformable mirror 3004 of FIG. 30or the CLC lens of FIG. 34) that reverses (e.g., by reflection ordiffraction) the direction of the light back toward the user's eye 4.

FIGS. 31A and 31B illustrate a reflective diffraction lens 3100A thatcan be implemented as part of a display device, where the reflectivediffraction lens 3100A is formed of patterned CLC materials serving as areflective polarizing mirror, in a similar manner to transmissive PB LClenses. FIG. 31A illustrates local orientations of liquid crystaldirectors (arrows) on top of a binary Fresnel lens pattern. Accordingly,the CLC lens 3100A can be configured to have optical power (which may beadjustable such as by an applied electric field). Embodiments of the CLClens 3100A can be used as an alternative to the deformable mirror 3004in the display of FIG. 30 or can be used to provide additionalreflectivity or optical power in the display of FIG. 30 (e.g., bycombining the CLC lens 3100A and the mirror 3004, e.g., via coating orlaminating the CLC lens onto a surface of the mirror 3004).

Referring to FIG. 31B, when the lens 3100A is illuminated withcircularly polarized incident light 3012 having a circular polarizationthat corresponds to (e.g., having the same handedness as) the handednessof the CLC chirality (e.g., RHCP), the reflected light 3016 exhibitslens effects similar to transmissive PB lenses. On the other hand, lightwith the orthogonal polarization (e.g., LHCP) is transmitted withoutinterference. The lens 3100A can be configured to have a bandwidth in arange of less than about 10 nm, less than about 25 nm, less than about50 nm, less than about 100 nm, or some other range.

FIG. 31C illustrates a reflective diffraction lens 3100C comprising aplurality of reflective diffraction lenses 3100-R, 3100-G and 3100-B. Inthe illustrated embodiment, the reflective diffraction lenses 3100-R,3100-G and 3100-B are in a stacked configuration and are configured toreflect light within a range of wavelengths Δλ within the red, green andblue spectra, respectively. When the lens 3100C is illuminated withcircularly polarized incident light 3012 having a circular polarizationthat corresponds to the handedness of the CLC chirality (e.g., RHCP) anda wavelength within a range of wavelengths Δλ within the red, green andblue spectra, the reflected light 3016 exhibits lens effects similar totransmissive PB lenses. On the other hand, light with the orthogonalpolarization (e.g., LHCP) is transmitted without interference.

Diffractive lenses (e.g., Fresnel lenses) often suffer from severechromatic aberration as the focal distances 3204 vary depending on thewavelength of light. This is illustrated in FIG. 32A with respect to adiffractive lens 3200A, which shows incident red, green, and blue lightbeing focused at different distances from the lens 3200A.

With benefit of moderate bandwidth of CLC materials, a stack of lensescan be implemented to have substantially the same focal distance fordifferent colors. FIG. 32B illustrates a reflective diffraction lens3200B comprising a plurality of reflective diffraction lenses 3200-R,3200-G and 3200-B in a stacked configuration similar to the reflectivediffraction lens 3100C illustrated with respect to FIG. 31C. As shown inFIG. 32B, the three individual lenses 3200-R, 3200-G and 3200-B aredesigned to have substantially the same focal distance or optical powerfor red, green, and blue wavelengths, respectively. Since the bandwidthof CLC materials is in many implementations around 50 nm to 100 nm,cross-talk between the three wavelengths can be reduced or minimized.Although 3 CLC layers are shown, fewer or greater numbers of layers canbe used corresponding to the colors of light incident on the lens 3200B.

Example Dynamic Switching Among CLC Lenses

FIG. 33A illustrates a reflective diffraction lens assembly 3300configured for dynamic switching between different focal distances. Thedynamic switching is achieved by stacking a plurality of reflectivediffraction lens sub-assemblies 3300-1, 3300-2 and 3300-3 comprisingfirst, second and third multi-layer diffraction lenses CLC L1, CLC L2and CLC L3, where each of the multi-layer diffraction lenses CLC L1, CLCL2 and CLC L3 comprises a plurality of lenses 3100-R, 3100-G and 3100-B.As configured, the reflective diffraction lens sub-assemblies 3300-1,3300-2 and 3300-3 are configured to have different focal distances. Theplurality of reflective diffraction lens sub-assemblies 3300-1, 3300-2and 3300-3 include first, second and third switchable half-wave platesHWP1, HWP2 and HWP3 (e.g., switchable LC half-wave plates). In theillustrated embodiment, the reflective diffraction lens sub-assemblies3300-1, 3300-2 and 3300-3 are in a stacked configuration such that themulti-layer diffraction lenses CLC L1, CLC L2 and CLC L3 of thesub-assemblies 3300-1, 3300-2 and 3300-3 alternate with switchablehalf-wave plates (HWP) of the sub-assemblies 3300-1, 3300-2 and 3300-3.

FIGS. 33B and 33C illustrate an example switching operation between twodifferent reflective diffraction lens sub-assemblies 3300-1 and 3300-2by modulating the HWPs disposed in each. When the first HWP (HWP1) is inan OFF-state (e.g., no retardation), light is reflected by the first CLClens (CLC L1) and the image focus is determined by the first CLC L1.When both HWP1 and HWP2 are in an ON state (e.g., half-waveretardation), light is not reflected from the CLC L1 as its polarizationbecomes orthogonal (e.g., LHCP) to the operating polarization (e.g.,RHCP). The polarization state is restored by the HWP2 and light isreflected from the CLC L2). The image focus is now determined by the CLCL2.

Similarly, three different focal distances can be implemented by addingadditional pair of CLC lens and HWP as shown in FIG. 33D. Lightpolarization is converted to the orthogonal polarization (e.g., LCHP) tothe operating polarization (e.g., RHCP) by the HWP1. Since the HWP2 isin an OFF state, the polarization is not affected and light propagatesthrough the CLC L2 without interference. After the HWP3, thepolarization is flipped again and becomes the operating polarization(e.g., RHCP) and light is reflected by the CLC L3. The image focus isnow determined by the CLC L3 as shown in FIG. 33D.

In embodiments, variable focus of virtual images can be implemented bycombining a waveguide assembly 3404 (also and a CLC lens 3408 asillustrated in FIG. 34. The CLC lens 3408 can include any of theembodiments of the CLC lenses 3100A, 3100C, 3200A, 3200B, 3300 describedherein. Since images projected from the waveguide assembly 3404propagate preferentially toward the CLC lens (e.g., world-ward, in thedirection away from the user's eyes) with uniform circular polarization,the image focus can be controlled by CLC lenses as described above. TheCLC lens 3408 can include multiple depth planes (e.g., DoF1-DoF3 shownin FIG. 33A) and be dynamically switchable as described with referenceto FIGS. 33B-33D. When a color-sequential display is used to generatevirtual images, the waveplates in CLC lenses need to be modulated insynchronization with operating colors projected by the eyepiece 3404. Asdescribed above, the CLC lens 3408 can be used alone or in combinationwith a deformable mirror (e.g., mirror 3004) to provide a variable focusdisplay device for virtual images.

Additional Aspects

In a 1^(st) aspect, a display device comprises a waveguide configured topropagate visible light under total internal reflection in a directionparallel to a major surface of the waveguide. An outcoupling element isformed on the waveguide and configured to outcouple a portion of thevisible light in a direction normal to the major surface of thewaveguide. A polarization-selective notch reflector disposed on a firstside of the waveguide and configured to reflect visible light having afirst polarization while transmitting visible light having a secondpolarization. A polarization-independent notch reflector disposed on asecond side of the waveguide and configured to reflect visible lighthaving the first polarization and visible light having the secondpolarization, where the polarization-independent notch reflector isconfigured to convert a polarization of visible light reflectingtherefrom.

In a 2^(nd) aspect, in the display device of the 1^(st) aspect, each ofthe polarization-selective notch reflector and thepolarization-independent notch reflector is configured to reflectvisible light having a wavelength in a wavelength range corresponding toone of red, green or blue light, while transmitting light having awavelength outside the wavelength range.

In a 3^(rd) aspect, in the display device of any of the 1^(st) to 2^(nd)aspects, the polarization-selective notch reflector comprises one ormore cholesteric liquid crystal (CLC) layers.

In a 4^(th) aspect, in the display device of any of the 1^(st) to 3^(rd)aspects, each of the one or more CLC layers comprises a plurality ofchiral structures, where each of the chiral structures comprises aplurality of liquid crystal molecules that extend in a layer depthdirection by at least a helical pitch and are successively rotated in afirst rotation direction. The helical pitch is a length in the layerdepth direction corresponding to a net rotation angle of the liquidcrystal molecules of the chiral structures by one full rotation in thefirst rotation direction. Arrangements of the liquid crystal moleculesof the chiral structures vary periodically in a lateral directionperpendicular to the layer depth direction.

In a 5^(th) aspect, in the display device of any of the 1^(st) to 4^(th)aspects, the first polarization is a first circular polarization and thesecond polarization is a second circular polarization.

In a 6^(th) aspect, in the display device of any of the 1^(st) to 5^(th)aspects, the display device further comprising a first quarter-waveplate and a second quarter-wave plate, wherein thepolarization-independent notch reflector is interposed between the firstquarter-wave plate and the waveguide, and wherein thepolarization-selective notch reflector is interposed between thewaveguide and the second quarter-wave plate.

In a 7^(th) aspect, in the display device of the 6^(th) aspect, thedisplay device further comprises a first linear polarizing lens and asecond linear polarizing lens, wherein the first quarter-wave plate isinterposed between the first linear polarizing lens and thepolarization-independent notch reflector, and wherein the secondquarter-wave plate is interposed between the polarization-selectivenotch reflector and the second linear polarizing lens.

In an 8^(th) aspect, in the display device of any of the 1^(st) to4^(th) aspects, the display device further comprises a firstPancharatnam-Berry (PB) lens and a second Pancharatnam-Berry (PB) lensdisposed on outer sides of the polarization-independent notch reflectorand the polarization-selective notch reflector.

In a 9^(th) aspect, in the display device of any of the 1^(st) or 2^(nd)aspects, the display device further comprises a first quarter-wave plateinterposed between the polarization-independent notch reflector and thewaveguide.

In a 10^(th) aspect, in the display device of the 9^(th) aspect, thedisplay device further comprises a second quarter-wave plate, whereinthe polarization-independent notch reflector is interposed between thefirst quarter-wave plate and the second quarter-wave plate.

In an 11^(th) aspect, in the display device of the 10^(th) aspect, thedisplay device further comprises a first linear polarizing lens and asecond linear polarizing lens, wherein the first quarter-wave plate isinterposed between the first linear polarizing lens and thepolarization-independent notch reflector, and wherein thepolarization-selective notch reflector is interposed between thewaveguide and the second linear polarizing lens.

In a 12^(th) aspect, in the display device of the 9^(th) aspect, thedisplay device further comprises a first Pancharatnam-Berry (PB) lens, asecond Pancharatnam-Berry (PB) lens disposed on outer sides of thepolarization-independent notch reflector and the polarization-selectivenotch reflector, and a second quarter-wave plate interposed between thesecond PB lens and the polarization-selective notch reflector.

In a 13^(th) aspect, a display device comprises a wave-guiding deviceinterposed between a first switchable lens and a second switchable lens.The wave-guiding device comprises one or more cholesteric liquid crystal(CLC) layers each comprising a plurality of chiral structures, whereineach chiral structure comprises a plurality of liquid crystal moleculesthat extend in a layer depth direction and are successively rotated in afirst rotation direction, wherein arrangements of the liquid crystalmolecules of the chiral structures vary periodically in a lateraldirection perpendicular to the layer depth direction such that the oneor more CLC layers are configured to Bragg-reflect incident light. Oneor more waveguides are formed over the one or more CLC layers andconfigured to propagate visible light under total internal reflection(TIR) in a direction parallel to a major surface of the waveguide and tooptically couple visible light to or from the one or more CLC layers.

In a 14^(th) aspect, in the display device of the 13^(th) aspect, theone or more waveguides are interposed between a polarization-selectivenotch reflector and a polarization-independent notch reflector, whereinthe polarization-selective notch reflector is configured to reflectvisible light having a first polarization while transmitting visiblelight having a second polarization, and wherein thepolarization-independent notch reflector is configured to reflectvisible light having the first polarization and visible light having thesecond polarization.

In a 15^(th) aspect, in the display device of the 13^(th) aspect, theone or more CLC layers serve as the polarization-selective notchreflector.

In a 16^(th) aspect, in the display device of the 13^(th) aspect, thepolarization-selective notch reflector comprises one or more cholestericliquid crystal (CLC) layers.

In a 17^(th) aspect, in the display device of the 16^(th) aspect, eachof the one or more CLC layers comprises a plurality of chiralstructures, wherein each of the chiral structures comprises a pluralityof liquid crystal molecules that extend in a layer depth direction by atleast a helical pitch and are successively rotated in a first rotationdirection. The helical pitch is a length in the layer depth directioncorresponding to a net rotation angle of the liquid crystal molecules ofthe chiral structures by one full rotation in the first rotationdirection. Arrangements of the liquid crystal molecules of the chiralstructures vary periodically in a lateral direction perpendicular to thelayer depth direction.

In an 18^(th) aspect, in the display device of any one of the 13^(th) to17^(th) aspects, the polarization-selective notch reflector isconfigured to preserve a polarization of visible light reflectingtherefrom, and wherein the polarization-independent notch reflector isconfigured to convert a polarization of visible light reflectingtherefrom.

In a 19^(th) aspect, in the display device of any one of the 13^(th) to18^(th) aspects, the first switchable lens and the second switchablelens have optical powers having opposite signs when activated.

In a 20^(th) aspect, in the display device of any one of the 13^(th) to19^(th) aspects, the first switchable lens comprises aPancharatnam-Berry (PB) lens and the second switch able lens comprises asecond Pancharatnam-Berry (PB) lens.

In a 21^(st) aspect, in the display device of any one of the 13^(th) to20^(th) aspects, the display device further comprises a firstquarter-wave plate interposed between the polarization-independent notchreflector and the waveguide.

In a 22^(nd) aspect, in the display device of any one of the 13^(th) to21^(st) aspects, the display device further comprises a secondquarter-wave plate interposed between the second switchable lens and thepolarization-selective notch reflector.

In a 23^(rd) aspect, a display device configured to display an image toan eye of a user comprises an optical display comprising a forward sideand a rearward side, the rearward side closer to the eye of the userthan the forward side, the optical display configured to output lighthaving a wavelength range toward the rearward side. A first notchreflector is disposed rearward of the optical display, the first notchreflector configured to reflect light having the wavelength range outputfrom the optical display. A second notch reflector is disposed forwardof the optical display, the second notch reflector configured to reflectlight having the wavelength range. The first notch reflector isconfigured to substantially transmit light having a first polarizationand substantially reflect light having a second polarization that isdifferent from the first polarization. The second notch reflector isconfigured to convert light incident on a rearward face having thesecond polarization to the first polarization and to redirect the lightrearward.

In a 24^(th) aspect, in the display device of the 23^(rd) aspect, thefirst notch reflector comprises a cholesteric liquid crystal (CLC)grating (CLCG).

In a 25^(th) aspect, in the display device of the 23^(rd) aspect, thefirst notch reflector comprises a multi-layer, and the second notchreflector comprises a non-polarizing notch reflector and a quarter-waveplate.

In a 26^(th) aspect, in the display device of any one of the 23^(rd) to25^(th) aspects, the display device further comprises a first variablefocus lens disposed rearward of the first notch reflector and a secondvariable focus lens disposed forward of the second notch reflector,wherein second optical characteristics of the second variable focus lenscompensate for first optical characteristics of the first variable focuslens.

In a 27^(th) aspect, in the display device of the 26^(th) aspect, eachof the first variable focus lens and the second variable focus lenscomprises a linear polarization lens.

In a 28^(th) aspect, in the display device of the 26^(th) aspect, eachof the first variable focus lens and the second variable focus lenscomprises a Pancharatnam-Berry (PB) phase lens.

In a 29^(th) aspect, in the display device of the 28^(th) aspect, thedisplay device further comprises a spatial offset compensator configuredto compensate for a spatial offset introduced by the PB phase lenses.

In a 30^(th) aspect, a dynamically focused display system comprises adisplay configured to output circularly polarized light in a firstcircular polarization state. The display is disposed along an opticalaxis and has a forward side and a rearward side, the rearward sidecloser to the eye of the user than the forward side, the optical displayconfigured to output light having a wavelength range toward the rearwardside. A first switchable optical element is disposed forward of thefirst CLC lens along the optical axis, the first switchable opticalelement configured to change the circular polarization state of lighttransmitted through the first switchable optical element from the firstcircular polarization state to a second, different, circularpolarization state. A first cholesteric liquid crystal (CLC) lens isdisposed forward of the first switchable optical element along theoptical axis. A second switchable optical element is disposed forward ofthe first CLC lens along the optical axis, the second switchable opticalelement configured to change the circular polarization state of lighttransmitted through the second switchable optical element from the firstcircular polarization state to a second, different, circularpolarization state. A second CLC lens disposed forward of the secondswitchable optical element along the optical axis. A controller isconfigured to electronically switch the states of the first and thesecond switchable optical elements to dynamically select either thefirst CLC lens or the second CLC lens.

In a 31^(st) aspect, in the dynamically focused display system of the30^(th) aspect, in response to selection of the first CLC lens, thefirst switchable optical element is switched to permit transmission oflight having the first polarization state. In response to selection ofthe second CLC lens, the first switchable optical element is switched tochange polarization of light from the first circular polarization stateto the second circular polarization state and the second switchableoptical element is switched to change polarization of light from thesecond circular polarization state to the first circular polarizationstate.

In a 32^(nd) aspect, in the dynamically focused display system of the30^(th) or 31^(st) aspects, the first and the second switchable opticalelements comprise half-wave plates.

In a 33^(rd) aspect, a wearable augmented reality display systemcomprises the dynamically focused display system of any one of the30^(th) to 32^(nd) aspects.

In a 34^(th) aspect, a wearable augmented reality head-mounted displaysystem is configured to pass light from the world forward a wearerwearing the head-mounted system into an eye of the wearer. The wearableaugmented reality head mounted display system comprises an opticaldisplay configured to output light to form an image; one or morewaveguides disposed to receiving said light from said display; a frameconfigured to dispose the waveguides forward of said eye such that saidone or more waveguides have a forward side and a rearward side, saidrearward said closer to said eye than said forward side; a cholestericliquid crystal (CLC) reflector disposed on said forward side of said oneor more waveguides, said CLC reflector configured to have an opticalpower or a depth of focus that is adjustable upon application of anelectrical signal; and one or more out-coupling elements disposed withrespect to said one or more waveguides to extract light from the one ormore waveguides and direct at least a portion of said light propagatingwithin said waveguide to the CLC reflector, said light being directedfrom said CLC reflector back through said waveguide and into said eye topresent an image from the display into the eye of the wearer.

In a 35^(th) aspect, a display device comprises a waveguide configuredto propagate visible light under total internal reflection in adirection parallel to a major surface of the waveguide and to outcouplethe visible light in a direction normal to the major surface. A notchreflector is configured to reflect visible light having a firstpolarization, wherein the notch reflector comprises one or morecholesteric liquid crystal (CLC) layers, wherein each of the CLC layerscomprises a plurality of chiral structures, wherein each of the chiralstructures comprises a plurality of liquid crystal molecules that extendin a layer depth direction and are successively rotated in a firstrotation direction, wherein arrangements of the liquid crystal moleculesof the chiral structures vary periodically in a lateral directionperpendicular to the layer depth direction such that the one or more CLClayers are configured to Bragg-reflect incident light.

In a 36^(th) aspect, in the display device of the 35^(th) aspect, thewaveguide is configured to outcouple the visible light selectivelytowards the notch reflector.

In a 37^(th) aspect, in the display device of the 35^(th) or 36^(th)aspects, the notch reflector comprises a deformable mirror having theone or more CLC layers formed (or disposed) thereon.

In a 38^(th) aspect, in the display device of any of one the 35^(th) to37^(th) aspects, different ones of the one or more CLC layers areconfigured to reflect visible light having a wavelength in a wavelengthrange corresponding to different ones of red, green or blue light, whilebeing configured to transmit light having a wavelength outside thewavelength range.

In a 39^(th) aspect, in the display device of any one of the 35^(th) to38^(th) aspects, each of the chiral structures of the CLC layerscomprises a plurality of liquid crystal molecules that extend in a layerdepth direction by at least a helical pitch, wherein different ones ofthe one or more CLC layers have different helical pitches.

In a 40^(th) aspect, in the display device of the 38^(th) or 39^(th)aspects, different ones of the one or more CLC layers have substantiallythe same optical power.

In a 41^(st) aspect, in the display device of any one of 35^(th) to40^(th) aspects, the display device comprises a plurality of notchreflectors, wherein each of the notch reflectors is configured toreflect visible light having a first polarization, wherein each of thenotch reflector comprises one or more cholesteric liquid crystal (CLC)layers, wherein each of the CLC layers comprises a plurality of chiralstructures, wherein each of the chiral structures comprises a pluralityof liquid crystal molecules that extend in a layer depth direction andare successively rotated in a first rotation direction, whereinarrangements of the liquid crystal molecules of the chiral structuresvary periodically in a lateral direction perpendicular to the layerdepth direction such that the one or more CLC layers are configured toBragg-reflect incident light.

In a 42^(nd) aspect, in the display device of any one of the 35^(th) to41^(st) aspects, different ones of the notch reflectors have differentoptical powers.

In a 43^(rd) aspect, in the display device of the 41^(st) or 42^(nd)aspects, the display device further comprises a half-wave platecorresponding to each of the notch reflectors.

Additional Considerations

In the embodiments described above, augmented reality display systemsand, more particularly, spatially varying diffraction gratings aredescribed in connection with particular embodiments. It will beunderstood, however, that the principles and advantages of theembodiments can be used for any other systems, apparatus, or methodswith a need for the spatially varying diffraction grating. In theforegoing, it will be appreciated that any feature of any one of theembodiments can be combined and/or substituted with any other feature ofany other one of the embodiments.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The word “coupled”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Likewise, the word “connected”, as generally used herein,refers to two or more elements that may be either directly connected, orconnected by way of one or more intermediate elements. Additionally, thewords “herein,” “above,” “below,” “infra,” “supra,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singularnumber, respectively. The word “or” in reference to a list of two ormore items, that word covers all of the following interpretations of theword: any of the items in the list, all of the items in the list, andany combination of one or more of the items in the list. In addition,the articles “a,” “an,” and “the” as used in this application and theappended claims are to be construed to mean “one or more” or “at leastone” unless specified otherwise.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: A, B, or C” is intended to cover: A, B, C,A and B, A and C, B and C, and A, B, and C. Conjunctive language such asthe phrase “at least one of X, Y and Z,” unless specifically statedotherwise, is otherwise understood with the context as used in generalto convey that an item, term, etc. may be at least one of X, Y or Z.Thus, such conjunctive language is not generally intended to imply thatcertain embodiments require at least one of X, at least one of Y and atleast one of Z to each be present.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or whether these features,elements and/or states are included or are to be performed in anyparticular embodiment.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, methods, andsystems described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. For example, while blocks arepresented in a given arrangement, alternative embodiments may performsimilar functionalities with different components and/or circuittopologies, and some blocks may be deleted, moved, added, subdivided,combined, and/or modified. Each of these blocks may be implemented in avariety of different ways. Any suitable combination of the elements andacts of the various embodiments described above can be combined toprovide further embodiments. The various features and processesdescribed above may be implemented independently of one another, or maybe combined in various ways. No element or combinations of elements isnecessary or indispensable for all embodiments. All suitablecombinations and subcombinations of features of this disclosure areintended to fall within the scope of this disclosure.

What is claimed is:
 1. A display device, comprising: a wave-guidingdevice interposed between a first switchable lens assembly and a secondswitchable lens assembly, wherein the wave-guiding device comprises: oneor more cholesteric liquid crystal (CLC) layers each comprising aplurality of chiral structures, wherein each chiral structure comprisesa plurality of liquid crystal molecules that extend in a layer depthdirection and are successively rotated in a first rotation direction,wherein arrangements of the liquid crystal molecules of the chiralstructures vary periodically in a lateral direction perpendicular to thelayer depth direction such that the one or more CLC layers areconfigured to Bragg-reflect incident light; and one or more waveguidesformed over the one or more CLC layers and configured to propagatevisible light under total internal reflection (TIR) in a directionparallel to a major surface of the waveguide and to optically couplevisible light to or from the one or more CLC layers.
 2. The displaydevice of claim 1, wherein the one or more waveguides are interposedbetween a polarization-selective notch reflector and apolarization-independent notch reflector, wherein thepolarization-selective notch reflector is configured to reflect visiblelight having a first polarization while transmitting visible lighthaving a second polarization, and wherein the polarization-independentnotch reflector is configured to reflect visible light having the firstpolarization and visible light having the second polarization.
 3. Thedisplay device of claim 2, wherein the one or more CLC layers serve asthe polarization-selective notch reflector.
 4. The display device ofclaim 2, wherein the polarization-selective notch reflector comprisesone or more CLC layers.
 5. The display device of claim 4, wherein eachof the one or more CLC layers of the polarization-selective notchreflector comprises a plurality of chiral structures, wherein each ofthe chiral structures comprises a plurality of liquid crystal moleculesthat extend in a layer depth direction by at least a helical pitch andare successively rotated in a first rotation direction, wherein thehelical pitch is a length in the layer depth direction corresponding toa net rotation angle of the liquid crystal molecules of the chiralstructures by one full rotation in the first rotation direction, andwherein arrangements of the liquid crystal molecules of the chiralstructures vary periodically in a lateral direction perpendicular to thelayer depth direction.
 6. The display device of claim 2, wherein thepolarization-selective notch reflector is configured to preserve apolarization of visible light reflecting therefrom, and wherein thepolarization-independent notch reflector is configured to convert apolarization of visible light reflecting therefrom.
 7. The displaydevice of claim 2, further comprising a first quarter-wave plateinterposed between the polarization-independent notch reflector and thewaveguide.
 8. The display device of claim 7, further comprising a secondquarter-wave plate interposed between the second switchable lens and thepolarization-selective notch reflector.
 9. The display device of claim1, wherein the first switchable lens and the second switchable lens haveoptical powers having opposite signs when activated.
 10. The displaydevice of claim 1, wherein the first switchable lens assembly comprisesa Pancharatnam-Berry (PB) lens and the second switchable lens assemblycomprises a second Pancharatnam-Berry (PB) lens.